This PDF file contains the front matter associated with SPIE Proceedings Volume 11946, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

Functional Near-InfraRed Spectroscopy (fNIRS) measures cerebral hemodynamics associated with brain activation. Non-invasive optical measurements of cerebral hemodynamics are often confounded by superficial, extra-cerebral hemodynamics and by instrumental and motion artifacts. These confounds are especially prominent in optical intensity data collected at a single source-detector distance. Alternatively, slope methods and frequency-domain measurements of the phase of photon-density waves have been proposed. Here, we first demonstrate the ability of a special slope method (dual-slope) to efficiently suppress instrumental artifacts. Then, a dual-slope imaging array is utilized to generate and compare single-distance and dual-slope intensity and phase data collected on the visual cortex of a human subject during a contrast reversing visual stimulation protocol. The measured hemodynamic traces associated with visual stimulation exhibit a larger amplitude when they are derived from dual-slope versus single-distance data, and from phase versus intensity data. In particular, the functional hemodynamics obtained from dual-slope phase data feature the largest amplitude. These results indicate the greater sensitivity to brain tissue achieved by dual-slope versus single-distance data, and by phase versus intensity data. The conclusion of this work is that dual-slope intensity (in continuous-wave fNIRS) and dual-slope or single-distance phase (in frequency-domain fNIRS) appear to be most effective for functional brain measurements, with the significant practical advantage offered by the minimal sensitivity of dual-slope measurements to a variety of artifacts.

Oxygen saturation (sO2) and blood perfusion in brain tissue have been known to be modulated with cellular activity in the brain. A single fiber system (SFS) has previously been shown to enable sO2 measurements from localized deep brain regions in freely moving animals. Reflectance spectra (RSF) obtained through the SFS can be used to understand changes in blood perfusion and fit to an empirical model to extract sO₂. The sO₂ extracted is dependent on the shape of RSF and thus relatively resistant to noise as compared to blood perfusion which is dependent on the magnitude of RSF at specific wavelengths. While slow changes in sO₂ have been shown to be robust, sources of certain relatively rapid temporal variations observed in the sO₂ signal remains unclear. Potential sources could be variations in cellular activity in the brain or noise due to motion artifacts. In this work, we have described the design of new experiments focused to investigate the effects of motion artifacts on RSF and sO₂. Computer simulations and mathematical modelling have been used to explain the experimental findings. Results suggest that the motion artifacts mainly arise from the fiber/brain interface and appear to offset RSF. Using the interpretation from a mathematical model, we also propose a motion artifact correction algorithm which can potentially be used for comparison of perfusion signals.

Image reconstruction with functional near infrared spectroscopy (fNIRS) and high density diffuse optical tomography (HD-DOT) rely on anatomical models that adequately capture the head size and shape for accurate data registration. Optical brain imaging studies in infants and toddlers without MRI present challenges in model generation because individual differences in scalp morphometry across early development lead to poor matches with atlas-based models. Additionally, current photometric methods are limited due to the presence of hair. We present herein the scalp surface estimation technique, validated with participant specific MRI, that accurately provides the head shape in the presence of hair.

We report the implementation and demonstration of an imaging system that combines two-photon phosphorescence lifetime microscopy (2PLM) and adaptive optics for improving oxygen partial pressure (pO₂) measurement accuracy in deep cortical layers of mice. The technique retrieves the background signal by forming an aberrated torus focus on the sample plane with an optical phase mask imposed on the system wavefront and subtracts it from normal phosphorescence emission signal. The proposed method is validated with intravascular pO₂ measurements from six mice imaged at up to ~600 μm depth.