The development and validation of hybrid frequency- domain and broadband diffuse optical spectroscopy for monitoring tissue water content during hemodialysis
Embargo Date
2026-07-29
OA Version
Citation
Abstract
Poor fluid management during hemodialysis in patients with end-stage kidney disease (ESKD) contributes to adverse clinical outcomes. Current clinical tools for assessing volume status, such as Crit-Line hematocrit monitoring, are limited in their predictive capability, underscoring the need for objective and quantitative measurement techniques. To address this gap, a frequency-domain and broadband near-infrared spectroscopy (FD-Bb-NIRS) system was developed to continuously and noninvasively monitor tissue optical properties in patients undergoing hemodialysis. The FD-Bb-NIRS system integrates frequency-domain (FD) and continuous-wave (CW) diffuse optical spectroscopy (DOS) measurements to recover absolute absorption and reduced scattering spectra over the 700 to 1000 nm. These measurements were integrated using model-based analysis to provide broadband absorption and reduced scattering spectra. Beer’s law was used to extract tissue chromophore concentrations. Across 27 hemodialysis sessions, the Water Ratio ([Water]/([Water] + [Lipid]) was the only chromophore based metric that was significantly different between subjects with (N=18) and without (N=9) intradialytic adverse events (p = 0.0313), with a decrease observed in patients without adverse events. Additionally, a multivariate discriminant analysis combining ΔWater Ratio, scattering amplitude (A) and slope (b) achieved the highest classification performance (AUC = 0.88). An analysis of these features also demonstrated predictive power at earlier timepoints, indicating potential for pre-symptomatic identification of patients at risk (AUC=0.93 at 25% dialysis completion, with respect to total dialysis time). While these results are promising, further improvements in tissue water quantification could enhance the accuracy of monitoring. To address this need, the FD-Bb-NIRS system was extended to incorporate measurements in the short-wave infrared (SWIR) range (900–1300 nm). Extending frequency domain diffuse optical spectroscopy (FD-DOS) into the short-wave infrared region has the potential to improve measurements of key biological tissue chromophores such as water and lipids, given their higher absorption in SWIR compared with near-infrared wavelengths. Few studies have explored FD-DOS in the SWIR range.
The first demonstration of a frequency domain broadband SWIR spectroscopy (FD-Bb-SWIRS) system was developed to measure optical properties from 685 to 1300 nm. A custom hybrid system was developed, combining frequency domain measurements from 685 to 980 nm at discrete wavelengths with broadband continuous wave measurements from 900 to 1300 nm. This setup provided absolute absorption (μa) spectra from 685 to 1300 nm. Validation was performed using mineral oil-based solid phantoms, deuterium oxide (D2O) liquid phantoms, and desiccating porcine tissue.
The FD-Bb-SWIRS system was sensitive to changes in μa from varying concentrations of absorbers in solid and liquid phantoms. Ex vivo measurements of μa spectra indicated differences in tissue water content across different porcine tissue samples during baseline and desiccation. μ_s^' values were within the anticipated range for both porcine tissue and phantom measurements. The FD-Bb-SWIRS system enables precise quantification of water in biological tissues. It represents a significant step forward in advancing SWIR-based optical spectroscopy for clinical applications.
Description
2026