Hyperspectral time-resolved compressive sensing spectroscopy for monitoring cytochrome-c-oxidase and blood oxygenation

Abstract

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.

HyperTRCSS: A hyperspectral time-resolved compressive sensing spectrometer for depth-sensitive monitoring of cytochrome-c-oxidase and blood oxygenation

“…However, NIR spectra acquired from tissue can be sparsely represented in the spectral domain; therefore, a CS approach can be applied to reconstruct the spectrum from fewer sampling patterns 55 . We previously demonstrated that there are no differences between estimations of changes in chromophore concentrations obtained from uncompressed and 90% compressed acquisitions 56 . Therefore, the data were sampled using a 90% compression rate to reduce the acquisition time for a full spectrum of distributions of time-of-flight (DTOFs) to 20 s, corresponding to an effective sampling rate of 0.05 Hz.…”

“…A DTOF collection time of 0.3 s was used along with a 0.05 s pause to ensure synchronicity between the DMD patterns and DTOF measurements. Note that DTOFs acquired outside of the 675 to 875 nm range had very low signal-to-noise ratio (SNR) and therefore were excluded from further analysis; the resulting spectra had 170 points and a resolution of 5.8 nm 56 . Further details regarding the spectral calibration procedure are included in the Supplementary Material for reference.…”

“…Blood-yeast liquid phantoms have been used to assess the ability of NIRS systems to estimate changes in Hb and HbO 50 , 59 – 61 and even oxCCO 56 , 62 . Here, we demonstrate HyperTRCSS monitoring of Hb, HbO, and oxCCO changes in homogeneous blood-yeast liquid phantoms with reference CW-NIRS measurements acquired concomitantly by a commercial spectrometer (Maya2000 Pro, Ocean Insight).…”

“…Δμ a ðλÞ was computed by subtracting the baseline μ a ðλÞ and then fit to Eq. ( 3) using a least-squares minimization approach 56 to estimate changes in chromophore concentrations, i.e., ΔHb, ΔHbO, and ΔoxCCO:…”

“…By applying high compression rates (up to 90%), the acquisition time per spectrum is reduced from several minutes to seconds. Recently, we have developed a hyperspectral TR CS spectrometer that can acquire 170-point spectra over 675 to 875 nm in 20 s while exhibiting no differences from spectra acquired without compression 56 . We hypothesize that this device is sensitive to dynamic changes in blood oxygenation and oxCCO in deep (>10 mm) tissue (e.g., adult brain) through a thick top layer (e.g., ECL).…”