Figure - available from: Scientific Reports
This content is subject to copyright. Terms and conditions apply.
![Example of measured and fitted attenuation spectra μt(λ) for samples with varying [tHb] (average spectrum per sample, error bars represent SD). The plotted scattering spectrum represents the average scattering contribution of all whole blood samples that were included in this study. (a) Attenuation spectra obtained by conventional sOCT. (b) Attenuation spectra obtained by combining focus tracking and zero-delay acquisition.](publication/336741162/figure/fig2/AS:959550874218497@1605786164298/Example-of-measured-and-fitted-attenuation-spectra-mtl-for-samples-with-varying-tHb.png)
Example of measured and fitted attenuation spectra μt(λ) for samples with varying [tHb] (average spectrum per sample, error bars represent SD). The plotted scattering spectrum represents the average scattering contribution of all whole blood samples that were included in this study. (a) Attenuation spectra obtained by conventional sOCT. (b) Attenuation spectra obtained by combining focus tracking and zero-delay acquisition.
Source publication
![(a) Measured versus expected [tHb] values for all samples...](publication/336741162/figure/fig3/AS:959550874189840@1605786164396/a-Measured-versus-expected-tHb-values-for-all-samples-averageSD-by-using_Q320.jpg)
The non-invasive quantification of total haemoglobin concentrations [tHb] is highly desired for the assessment of haematologic disorders in vulnerable patient groups, but invasive blood sampling is still the gold standard in current clinical practice. This work demonstrates the potential of visible-light spectroscopic optical coherence tomography (...
Citations
... A visible-light optical coherence tomography (OCT) system with a center wavelength of 550 nm and an axial resolution of 2.3 µm was used to characterize the thickness and refractive index of the polyurethane films, similar to the approach of Sorin and Gray [42]. The details of this home-built system are described in our previous work [43][44][45]. To quantify both thickness and refractive index, a small opening was cut in the phantom and it was placed on a glass slide, as schematically illustrated in Fig. 1(C). ...
We propose a new, user-friendly and accessible approach for fabricating thin phantoms with controllable absorption properties in magnitude, spectral shape, and spatial distribution. We utilize a standard office laser color printer to print on polyurethane thin films (40 – 60 μm), commonly available as medical film dressings and ultrasound probe covers. We demonstrate that the optical attenuation and absorption of the printed films correlate linearly with the printer input settings (opacity), which facilitates a systematic phantom design. The optical and acoustic properties of these polyurethane films are similar to biological tissue. We argue that these thin phantoms are applicable to a wide range of biomedical applications. Here, we introduce two potential applications: (1) homogeneous epidermal melanin phantoms and (2) spatially resolved absorbers for photoacoustic imaging. We characterize the thin phantoms in terms of optical properties, thickness, microscopic structure, and reproducibility of the printing process.
... Recently, we showed how SDR 25 and SDBG 26 contaminate spectroscopic measurements in imaging ex vivo blood samples and in vivo human retinas. LCA (illustrated by the green, yellow, and red colors in the scanning beam in Fig. 1) has also been shown as a contaminant for structural and spectroscopic OCT [27][28][29] . ...
... We can modify the fitted scattering coefficient by multiplying it with the factor SSF. However, the value of SSF in vis-OCT varies significantly among different studies 16,19,27,56 . Recently, we determined using Monte Carlo simulation and experimental validation that our vis-OCT system measures an SSF near 0.06 55 . ...
Background
Retinal oxygen saturation (sO2) provides essential information about the eye’s response to pathological changes that can result in vision loss. Visible-light optical coherence tomography (vis-OCT) is a noninvasive tool that has the potential to measure retinal sO2 in a clinical setting. However, its reliability is currently limited by unwanted signals referred to as spectral contaminants (SCs), and a comprehensive strategy to isolate true oxygen-dependent signals from SCs in vis-OCT is lacking.
Methods
We develop an adaptive spectroscopic vis-OCT (ADS-vis-OCT) technique that can adaptively remove SCs and accurately measure sO2 under the unique conditions of each vessel. We also validate the accuracy of ADS-vis-OCT using ex vivo blood phantoms and assess its repeatability in the retina of healthy volunteers.
Results
In ex vivo blood phantoms, ADS-vis-OCT agrees with a blood gas machine with only a 1% bias in samples with sO2 ranging from 0% to 100%. In the human retina, the root mean squared error between sO2 values in major arteries measured by ADS-vis-OCT and a pulse oximeter is 2.1% across 18 research participants. Additionally, the standard deviations of repeated ADS-vis-OCT measurements of sO2 values in smaller arteries and veins are 2.5% and 2.3%, respectively. Non-adaptive methods do not achieve comparable repeatabilities from healthy volunteers.
Conclusions
ADS-vis-OCT effectively removes SCs from human images, yielding accurate and repeatable sO2 measurements in retinal arteries and veins with varying diameters. This work could have important implications for the clinical use of vis-OCT to manage eye diseases.
... Created with Bio-Render.com. levels 45 ). As a consequence, any variations observed in the spectrum are related to the hemoglobin/hemozoin conversion due to the presence of malaria parasites. ...
Malaria is one of the most life-threatening infectious diseases worldwide, claiming half a million lives yearly. Prompt and accurate diagnosis is crucial for disease control and elimination. Currently used diagnostic methods require blood sampling and fail to detect low-level infections. At the symptomatic stage of infection, the parasites feed on red blood cells' (RBCs) hemoglobin, forming inert crystals, the hemozoin, in the process. Thus, along with parasite maturation inside the RBCs, the hemoglobin and hemozoin proportion is inversely related, and they generate specific optical spectra, according to their concentration. Herein, to address the issues of finger prick sampling and the lack of sensitivity of the parasitological test, we explored the optical features of Plasmodium falciparum-infected RBCs through absorbance and reflectance spectrophotometric characterization, aiming for their detection. This is the first work fully characterizing the spectrophotometric properties of P. falciparum-infected RBCs by using only 16 specific wavelengths within the visible optical spectra and two different post-processing algorithms. With such an innovative methodology, low-level infections can be detected and quantified, and early- and late-stage development can be clearly distinguished, not only improving the current detection limits but also proving the successful applicability of spectrophotometry for competitive and accurate malaria diagnosis.
... These capabilities extend to whole blood (further referred to as blood), where absorption and scattering are wavelength-dependent and oxygen-dependent [9][10][11][12]. Applying short-time Fourier transforms (STFTs), OCT can measure wavelength-dependent attenuations of blood with micrometer-scale depth resolution, enabling the measurement of oxygen saturation (sO 2 ) in discrete blood vessels [13][14][15][16][17]. Studies suggested that alterations in retinal sO 2 can be a sensitive biomarker for blindness-causing diseases, including glaucoma and diabetic retinopathy [18,19]. ...
The optical properties of blood encode oxygen-dependent information. Noninvasive optical detection of these properties is increasingly desirable to extract biomarkers for tissue health. Recently, visible-light optical coherence tomography (vis-OCT) demonstrated retinal oxygen saturation (sO2) measurements by inversely measuring the oxygen-dependent absorption and scattering coefficients of whole blood. However, vis-OCT may be sensitive to optical scattering properties of whole blood, different from those reported in the literature. Incorrect assumptions of such properties can add additional uncertainties or biases to vis-OCT’s sO2 model. This work investigates whole blood’s scattering coefficient measured by vis-OCT. Using Monte Carlo simulation of a retinal vessel, we determined that vis-OCT almost exclusively detects multiple-scattered photons in whole blood. Meanwhile, photons mostly forward scatter in whole blood within the visible spectral range, allowing photons to maintain ballistic paths and penetrate deeply, leading to a reduction in the measured scattering coefficient. We defined a scattering scaling factor (SSF) to account for such a reduction and found that SSF varied with measurement conditions, such as numerical aperture, depth resolution, and depth selection. We further experimentally validated SSF in ex vivo blood phantoms with pre-set sO2 levels and in the human retina, both of which agreed well with our simulation.
... The result of our Cramér-Rao analysis using the system parameters in Ref. 23 can be found in Appendix D. Promising clinical applications include spectroscopic OCT, 28 where the attenuation coefficient is measured at multiple wavelengths to determine, e.g., oxygen saturation 29 and hemoglobin concentration. 30 Endeavors to measure water content 31 and glucose levels 32-34 based on the attenuation coefficient have also been undertaken. The precision with which these physiological properties can be determined, and the corresponding diagnostic relevance of such approaches squarely depends on the precision of the attenuation coefficient measurement. ...
Significance:
Optical coherence tomography (OCT) is an interferometric imaging modality, which provides tomographic information on the microscopic scale. Furthermore, OCT signal analysis facilitates quantification of tissue optical properties (e.g., the attenuation coefficient), which provides information regarding the structure and organization of tissue. However, a rigorous and standardized measure of the precision of the OCT-derived optical properties, to date, is missing.
Aim:
We present a robust theoretical framework, which provides the Cramér -Rao lower bound σμOCT for the precision of OCT-derived optical attenuation coefficients.
Approach:
Using a maximum likelihood approach and Fisher information, we derive an analytical solution for σμOCT when the position and depth of focus are known. We validate this solution, using simulated OCT signals, for which attenuation coefficients are extracted using a least-squares fitting procedure.
Results:
Our analytical solution is in perfect agreement with simulated data without shot noise. When shot noise is present, we show that the analytical solution still holds for signal-to-noise ratios (SNRs) in the fitting window being above 20 dB. For other cases (SNR<20 dB, focus position not precisely known), we show that the numerical calculation of the precision agrees with the σμOCT derived from simulated signals.
Conclusions:
Our analytical solution provides a fast, rigorous, and easy-to-use measure for OCT-derived attenuation coefficients for signals above 20 dB. The effect of uncertainties in the focal point position on the precision in the attenuation coefficient, the second assumption underlying our analytical solution, is also investigated by numerical calculation of the lower bounds. This method can be straightforwardly extended to uncertainty in other system parameters.
... Tissue absorption and scattering coefficients are strongly influenced by hemoglobin absorption, 59 oxygen saturation (SAT O 2 ) especially above 600 nm, 60 and melanin content. 23 Hence, these coefficients can be employed to qualitatively and quantitatively assist skin hemodynamics and inflammation. ...
Hydrotherapy is a traditional clinical practice that has been widely used for pain relief. However, immersion in hot water influences skin's moisture and morphology. In this study, we investigate the physiological changes of ex‐vivo chicken skin immersed in hot water (at 40 and 50°C) via monitoring the change in its absorption and scattering properties using the spatial frequency domain imaging (SFDI) technique. The procedure started by calculating the modulation transfer function of the proposed imaging system over a range of spatial frequencies using a high‐resolution test target. Thereafter, structured illumination patterns at different spatial frequencies were projected onto the examined samples via a reflective phase‐only spatial light modulator using transmission and reflection modes. The transmission and reflection images were recorded using a digital camera to reconstruct the optical absorption and scattering parameters. Such parameters were calculated using Kubelka–Munk and lookup table methods. For system validation, the optical properties of two kinds of milk (skimmed and full cream), as reference samples, were reconstructed using the proposed SFDI system in the reflection mode via lookup table method. The results revealed an increase in the scattering coefficient of the skin samples immersed in higher water temperature, while the absorption coefficient values were nearly the same. Furthermore, the obtained results were validated using Monte‐Carlo method showing absolute errors that range from 0.004 to 0.057. In conclusion, the proposed system was presented to investigate the changes in ex‐vivo skin properties under thermal‐hydrotherapy in the context of measured changes in optical parameters.
... However, reported vis-OCT oximetry methods accounted for blood's μs differently, among which significant discrepancies exist [7,22,23,31,[33][34][35][36]. Since vis-OCT oximetry fits the measured spectrum to the literature-reported μa and μs, deviations between the measured and reported μs can introduce sO2 measurement error. ...
Optical properties of blood encode oxygen-dependent information. Noninvasive optical detection of these properties is increasingly desirable to extract biomarkers for tissue health. Recently, visible-light optical coherence tomography (vis-OCT) demonstrated retinal oxygen saturation (sO 2 ) measurements using the depth-resolved spectrum of blood. Such measurements rely on differences between the absorption and scattering coefficients of oxygenated and deoxygenated blood. However, there is still broad disagreement, both theoretically and experimentally, on how vis-OCT measures blood’s scattering coefficient. Incorrect assumptions of blood’s optical properties can add additional uncertainties or biases into vis-OCT’s sO 2 model. Using Monte Carlo simulation of a retinal vessel, we determined that vis-OCT almost exclusively detects multiple-scattered photons in blood. Meanwhile, photons mostly forward scatter in blood within the visible spectral range, allowing photons to maintain ballistic paths and penetrate deeply, leading to a reduction in the measured scattering coefficient. We defined a scattering scaling factor (SSF) to account for such a reduction and found that SSF varied with measurement conditions, such as numerical aperture, depth resolution, and depth selection. We further experimentally validated SSF in ex vivo blood phantoms pre-set sO 2 levels and in the human retina, both of which agreed well with our simulation.
... In a recent work, we demonstrated the feasibility of [tHb] measurements with sOCT in ex-vivo human whole blood in the clinical range (7-23 g/dL) [1]. In that work, the retrieved [tHb] based on conventional sOCT achieved low precision (9.1 g/dL with a bias of 1.5 g/dL) compared to a commercial blood analyser. ...
... We used a custom-built sOCT described in our previous work [1,2] and depicted in Fig. 1. Briefly, the light from a supercontinuum broadband source was expanded and collimated by a set of three lenses. ...
... Light reflected at the reference mirror and backscattered by blood combined at the beam splitter and was guided into a custom-built spectrometer that had a spectral resolution δ λ = 0.1 nm in the range 460 -650 nm. We analysed ex-vivo human whole-blood as in our previous work [1]. Blood samples were prepared from six healthy donors of the Experimental Centre for Technical Medicine of the University of Twente. ...
... For SD, the signal within the blood vessel is buried in the noise floor. Meanwhile, the reduced noise floor in BD reveals the characteristic blood signal decay [30,31]. The attenuation is visible across the entire depth of the vessel. ...
Increases in speed and sensitivity enabled rapid clinical adoption of optical coherence tomography (OCT) in ophthalmology. Recently visible-light OCT (vis-OCT) achieved ultrahigh axial resolution, improved tissue contrast, and new functional imaging capabilities, demonstrating the potential to improve clincal care further. However, limited speed and sensitivity caused by the high relative intensity noise (RIN) in supercontinuum lasers impeded the clinical adoption of vis-OCT. To overcome these limitations, we developed balanced-detection vis-OCT (BD-vis-OCT), which uses two calibrated spectrometers to cancel noises common to sample and reference arms, including RIN. We analyzed the RIN to achieve a robust pixel-to-pixel calibration between the two spectrometers and showed that BD-vis-OCT enhanced system sensitivity by up to 22.2 dB. We imaged healthy volunteers at an A-line rate of 125 kHz and a field-of-view as large as 10 mm x 4 mm. We found that BD-vis-OCT revealed retinal anatomical features previously obscured by the noise floor.
... The attenuation coefficient µ t ( ) quantifies the rate at which light is attenuated per unit length when it interacts with a medium. Under the assumption of single scattering, the total attenuation µ t ( ) = µ a ( ) + µ s ( ) arises from absorption and scattering events, which are expressed in terms of coefficients µ a ( ) and µ s ( ) respectively 17,37 . A power-law describes the scattering coefficient µ s ( ) 27,29 , µ s ( ) = a −b , where b is known as the scattering power and a is a scaling factor. ...
... Human blood samples. We processed an existing set of data that was acquired from ex-vivo human whole-blood samples, initially analysed in our previous work 17 . Measurement setup and acquisition settings were thus identical to our previous work. ...
... Focus tracking and zero-delay acquisition. We also processed data acquired with FZA, introduced in our previous work 17,37,40 . In this acquisition scheme, the signal losses due to system attenuation (roll-off and defocus) are compensated experimentally during acquisition. ...
Spectroscopic optical coherence tomography (sOCT) has emerged as a new possibility for non-invasive quantification of total haemoglobin concentrations [tHb]. Recently, we demonstrated that [tHb] measured in ex-vivo human whole-blood with a conventional sOCT system achieves a precision of 9.10 g/dL with a bias of 1.50 g/dL. This precision improved by acquiring data with a combination of focus tracking and zero-delay acquisition (FZA) that compensated for experimental limitations, increasing to 3.80 g/dL with a bias of 1.50 g/dL. Nevertheless, sOCT precision should improve at least to ∼2 g/dL to be clinically relevant. Therefore, sOCT-based [tHb] determinations require the development of new analysis methods that reduce the variability of [tHb] estimations. In this work, we aim to increase sOCT precision by retrieving the [tHb] content from a numerical optimisation of the optical density (OD), while considering the blood absorption flattening effect. The OD-based approach simplifies previous two-step Lambert–Beer fitting approaches to a single step, thereby reducing errors during the fitting procedure. We validated our model with ex-vivo [tHb] measurements on flowing whole-blood samples in the clinical range (7–23 g/dL). Our results show that, with the new model, conventional sOCT can determine [tHb] with a precision of 3.09 g/dL and a bias of 0.86 g/dL compared to a commercial blood analyser. We present further precision improvement by combining the OD methodology with FZA, leading to a precision of 2.08 g/dL with a bias of 0.46 g/dL.
