Time-resolved (TR) near-infrared spectroscopy (NIRS) is a promising technique for neuromonitoring, but there are currently very few TR-NIRS devices with the spectral range and resolution needed for accurate monitoring of cerebral blood oxygenation (S t O 2 ) and metabolism (cytochrome-c-oxidase; oxCCO). Here we present a hyperspectral TR compressive sensing spectrometer with a wide spectral range, high spectral resolution, and no afterpulsing. A homogeneous blood-yeast phantom experiment was performed to evaluate the spectrometer's ability to monitor S t O 2 and oxCCO with and without compression. The effect of using a 90% compression rate on the recovered changes in deoxyhemoglobin (Hb), oxyhemoglobin (HbO), and oxCCO concentrations was investigated. No meaningful differences were found between concentration changes recovered from uncompressed and compressed data, with mean differences of 0.16 ± 0.20 µM , -0.25 ± 0.21 µM , and -0.04 ± 0.10 µM for Hb, HbO, and oxCCO, respectively. The results show that changes in oxCCO and S t O 2 can be reliably monitored with a high compression rate. Future work will compare the performance of the TR spectrometer with that of a continuous-wave spectrometer to assess accuracy and will investigate the sensitivity of the device to oxCCO and S t O 2 changes in the bottom compartment of a 2-layer tissue-mimicking phantom.
Near-infrared spectroscopy (NIRS) can measure tissue blood content and oxygenation; however, its use for adult neuromonitoring is challenging due to significant contamination from their thick extracerebral layers (ECL; primarily scalp and skull). This report presents a fast method for accurate estimation of adult cerebral blood content and oxygenation from hyperspectral time resolved NIRS (trNIRS) data. A two-phase fitting method, based on a two-layer head model (ECL and brain), was developed. Phase 1 uses spectral constraints to accurately estimate the baseline blood content and oxygenation in both layers, which are then used by Phase 2 to correct for the ECL contamination of the late-arriving photons. The method was validated with in silico data from Monte-Carlo simulations of hyperspectral trNIRS in a realistic model of the adult head obtained from a high-resolution MRI. Phase 1 recovered cerebral blood oxygenation and total hemoglobin with an accuracy of 2.7 ± 2.5 and 2.8 ± 1.8%, respectively, with unknown ECL thickness, and 1.5 ± 1.4 and 1.7 ± 1.1% when the ECL thickness was known. Phase 2 recovered these parameters with an accuracy of 1.5 ± 1.5 and 3.1 ± 0.9%, respectively. Future work will include further validation in tissue-mimicking phantoms with various top layer thicknesses and in a pig model of the adult head before human applications.
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