SignificanceHyperspectral time-resolved (TR) near-infrared spectroscopy offers the potential to monitor cytochrome-c-oxidase (oxCCO) and blood oxygenation in the adult brain with minimal scalp/skull contamination. We introduce a hyperspectral TR spectrometer that uses compressive sensing to minimize acquisition time without compromising spectral range or resolution and demonstrate oxCCO and blood oxygenation monitoring in deep tissue.AimDevelop a hyperspectral TR compressive sensing spectrometer and use it to monitor oxCCO and blood oxygenation in deep tissue.ApproachHomogeneous tissue-mimicking phantom experiments were conducted to confirm the spectrometer’s sensitivity to oxCCO and blood oxygenation. Two-layer phantoms were used to evaluate the spectrometer’s sensitivity to oxCCO and blood oxygenation in the bottom layer through a 10 mm thick static top layer.ResultsThe spectrometer was sensitive to oxCCO and blood oxygenation changes in the bottom layer of the two-layer phantoms, as confirmed by concomitant measurements acquired directly from the bottom layer. Measures of oxCCO and blood oxygenation by the spectrometer were highly correlated with “gold standard” measures in the homogeneous and two-layer phantom experiments.ConclusionsThe results show that the hyperspectral TR compressive sensing spectrometer is sensitive to changes in oxCCO and blood oxygenation in deep tissue through a thick static top layer.
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 (StO2) 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 after pulsing. A homogeneous blood-yeast phantom experiment was performed to evaluate the spectrometer’s ability to monitor StO2 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 StO2 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 StO2 changes in the bottom compartment of a 2-layer tissue-mimicking phantom.
Time-resolved Near-Infrared Spectroscopy (trNIRS) methods typically use multiple wavelengths and source-detector distances in conjunction with a solution of the diffusion approximation to quantify tissue blood content and oxygenation. This approach can be both computationally intensive and costly, as multiple detectors are required. We propose a novel two-layer fitting approach for multi-wavelength trNIRS, which uses a single detector while providing accurate estimates of cerebral oxygen saturation (ScO2) and hemoglobin content. The method uses a multi-step fitting algorithm to establish rough estimates of the absorption and scattering coefficients in the extracerebral layer and the brain, and subsequently refine those estimates, to improve accuracy while reducing crosstalk and complexity. Validation was conducted using Monte Carlo simulations in a realistic adult head model with appropriate optical properties at 680nm, 750nm, 800nm, and 830nm. The detector was located 30 mm anteriorly from the source, which was placed 50 mm above the right temple. Scalp oxygen saturation (SO2) (50%, 60%, and 70%) and ScO2 (40%-80%, 2% increments) were varied independently. The recovered ScO2 had a difference (mean±standard deviation) of 2.31±2.93% from inputted values, and cerebral total hemoglobin was recovered with a difference of 2.94±3.47%. Such high accuracy demonstrates the robustness of this computationally efficient two-layer fitting approach for analyzing multi-wavelength trNIRS measurements acquired with a single detector. Future work will involve validating the technique in tissue mimicking phantoms and animal studies.
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