Abstract
We developed a ratiometric method capable of estimating total hemoglobin concentration from optically measured diffuse reflectance spectra. The three isosbestic wavelength ratio pairs that best correlated to total hemoglobin concentration independent of saturation and scattering were 545/390, 452/390, and 529/390 nm. These wavelength pairs were selected using forward Monte Carlo simulations which were used to extract hemoglobin concentration from experimental phantom measurements. Linear regression coefficients from the simulated data were directly applied to the phantom data, by calibrating for instrument throughput using a single phantom. Phantoms with variable scattering and hemoglobin saturation were tested with two different instruments, and the average percent errors between the expected and ratiometrically-extracted hemoglobin concentration were as low as 6.3%. A correlation of r = 0.88 between hemoglobin concentration extracted using the 529/390 nm isosbestic ratio and a scalable inverse Monte Carlo model was achieved for in vivo dysplastic cervical measurements (hemoglobin concentrations have been shown to be diagnostic for the detection of cervical pre-cancer by our group). These results indicate that use of such a simple ratiometric method has the potential to be used in clinical applications where tissue hemoglobin concentrations need to be rapidly quantified in vivo.
Highlights
Hemoglobin (Hb) concentration is a metric used for many applications in the medical field, including anemia diagnosis and transfusion guidance
The goal of this study was to identify a set of isosbestic ratios that were best correlated to Hb concentration independent of scattering and Hb saturation
The optical ratios were averaged over all scattering levels for a given Hb concentration in the simulations
Summary
Hemoglobin (Hb) concentration is a metric used for many applications in the medical field, including anemia diagnosis and transfusion guidance. The current strategy for determining Hb concentration is an invasive procedure where blood is drawn from an artery and sent to a laboratory for further analysis. This process is time-consuming, subject to operator error, and carries the risk of infection. The need exists for a noninvasive technique that can rapidly and accurately predict Hb concentration in human and/or animal tissues If such a device and method were portable, it would have wide applicability in various areas where rapid Hb measurements are required, such as in the emergency or operating room, in the back of an ambulance, in the battlefield, and in other resource-limited settings. Ratiometric optical spectroscopy could be used to provide noninvasive longitudinal monitoring of neovascularization
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