Quantification of total hemoglobin concentrations [tHb] is imperative to determine blood-related diseases such as anemia. In this work, we validate [tHb] estimates by visible-light spectroscopic optical coherence tomography (vis-sOCT) with the gold standard, intravenous blood sample analysis from a commercial avoximeter. We recruited a group of 27 volunteers and retrieved [tHb] with vis-sOCT data from the microcirculation in the skin of the left posterior forearm. Expected [tHb] were obtained from blood sample analysis by a commercial analyzer. We compare the [tHb] estimated by vis-sOCT with the expected [tHb]. Additionally, the effect of multiple factors of influence such as gender, skin tone, and epidermal thickness is investigated.
Objective: We examined the impact of skin color on transcutaneous bilirubin (TcB) measurements in vitro.
Methods: Using layered neonatal skin mimicking phantoms with varying dermal bilirubin levels and epidermal melanosome volume fractions, the relationship between skin color and TcB precision is systematically investigated. TcB measurements were performed with a commercially available bilirubin meter (JM-105, Draeger Medical, Lubeck, Germany).
Results: Epidermal melanosome volume fractions affected TcB measurements, leading to larger underestimations at higher melanosome volume fractions and bilirubin levels. In this in vitro setting, underestimations ranged from 30 to 131 µmol/L at a TcB value of 250 µmol/L.
Conclusion: Skin pigmentation affects TcB accuracy, with greater underestimations observed in darker skin tones and higher bilirubin levels. Our results highlight the need for improved TcB meter design and cautious interpretation of TcB readings on newborns with dark skin.
Measurements of human milk fat content are essential for lactation care and research. We propose to quantify milk fat in non-homogenized human milk based on angular light scattering. Therefore, we measured the angular scattering profiles of milk from five donors using a goniometric light scattering setup. We also measured the milk fat globule (MFG) size distributions with 3D confocal laser scanning microscopy and use this as input in a Monte Carlo simulation. Both experimental and simulated angular scattering profiles are strongly dependent on fat concentration. The effect of the MFG size distribution on the scattering profiles will be discussed.
Thrombus formation is a physiological response to damage in a blood vessel. Monitoring thrombus formation is challenging, due to the limited imaging options available to analyze flowing blood. In this work, we use a visible-light optical coherence tomography (vis-OCT) system to monitor the dynamic process of the formation of thrombi in a microfluidic blood vessel-on-chip (VoC) device. Inside the VoC, thrombi form in a monolayered channel of endothelial cells perfused by human whole blood. We show that the correlation of the vis-OCT signal can be utilized as a marker for thrombus formation and can track and quantify its growth over time. We validate our results with fluorescence microscopic imaging of fibrin and platelets.
We propose a novel and accessible approach for fabricating thin phantoms with controllable absorption properties in terms of magnitude, spectral shape, and spatial distribution. The method involves a standard laser printer to print on thin polyurethane films emulating optical properties of biological tissue. We characterize the thin phantoms in terms of optical properties, thickness, microscopic structure, and reproducibility of the printing process. We argue that these thin phantoms hold potential for a wide range of biomedical applications and will discuss their potential application in transcutaneous bilirubinometry performance studies.
In this work, we developed a methodology to non-invasively quantify total hemoglobin [tHb] concentrations in the microcirculation of the skin with visible-light spectroscopic optical coherence tomography (vis-sOCT). Our approach is based on the spatial distribution of [tHb] inside a vis-sOCT scan. Local [tHb] are retrieved by analyzing the optical density at each point of the tomogram. We show that the [tHb] distribution map, termed hemogram, presents blood vessel distributions comparable to that of optical coherence tomography angiography. In addition, we obtain a clinically useful measurement of the average [tHb] by analyzing the [tHb] across the hemogram. For a healthy volunteer, this average [tHb] of 11.62 g/dL falls within the expected clinical range and is consistent between eight independent measurement locations on the skin with a standard deviation of 0.88 g/dL.
We present a novel processing technique to retrieve total haemoglobin concentrations with spectroscopic optical coherence tomography data based on numerical optimization of the optical density. We validated our method with ex-vivo human whole blood.
Breastfeeding plays a crucial role in public health, but relatively few imaging and sensing technologies are employed to study human lactation physiology. As a consequence, many breastfeeding problems are not well understood. We hypothesize that diffuse optical spectroscopic
imaging (DOSI) can potentially reveal important physiological parameters that help to define milk synthesis and secretion: glandular tissue content, hemodynamics and milk ejection. The aim of this study is to investigate the sensitivity of DOSI to these physiological parameters in (i) a case study (1 subject) on mammary involution of the lactating breast to its pre-pregnant state and (ii) a pilot study during milk extraction with a breast pump (4 lactating subjects, 5 non-lactating subjects). For the case study, the measured changes in the DOSI parameters (water, lipid, hemoglobin concentration) were consistent with the gradual replacement of fibro-glandular tissue by adipose tissue and vascular regression during mammary involution. For the pilot study, the measured changes in the DOSI parameters correlated with the extracted milk volume and occurrence of the milk ejection reflex. In conclusion, DOSI is sensitive to human lactation physiology, which can potentially aid to obtaining an in-depth understanding on the origin and treatment of breastfeeding problems.
Fat in human milk forms the main energy source for infants and is the most variable component in terms of concentration and composition. Knowledge on changes in human milk lipid composition and conformational state during a single breastfeed contributes to an in-depth understanding of lipid synthesis in the mammary gland. Therefore, the objective of this study was to evaluate the differences in fatty acid length, degree of unsaturation (lipid composition) and lipid
phase (lipid conformational state) of milk released at different stages during a breastfeed (fore-, bulk- and hindmilk). A total of 30 samples from 10 lactating subjects were investigated using confocal Raman spectroscopy. No significant differences in lipid composition were observed between fore-, bulk- and hindmilk samples, which is consistent with literature. A new finding from this study is that the lipid conformational state in human fore-, bulk- and hindmilk was
significantly different at room temperature. The lipid phase of foremilk was almost crystalline and the lipid phase of hindmilk was almost liquid. Based on this observation, we hypothesize that lipid synthesis in the mammary gland changes during a single breastfeed.
Significance. Quantifying human milk composition is important for daily nutritional management in neonatal intensive cares worldwide. Photonic solutions based on visible light can potentially aid in this analysis, as energy content of human milk depends largely on fat content, and the optical scattering properties of human milk predominantly depend on the size and concentration of fat globules. However, it is expected that human milk scattering changes upon homogenization, routinely done before analysis, which may affect fat globule size.
Aim. The first aim of this study was to investigate how the most common homogenization methods (gently inverting by hand, vortexing, and sonication) affect the optical properties of human milk. The second aim was to estimate the scattering contribution of casein micelles, the second most dominant scatterers in human milk.
Approach. We combined diffuse reflectance spectroscopy with spectroscopic optical coherence tomography to measure the scattering coefficient μs, reduced scattering coefficient μs′, and anisotropy g between 450 and 600 nm.
Results. Sonication induced the strongest changes in μs, μs′, and g compared to the gently inverted samples (203%, 202%, and 7%, respectively, at 550 nm), but also vortexing changed μs′ with 20%. Although casein micelles only showed a modest contribution to μs and g at 550 nm (7% and 1%, respectively), their contribution to μs′ was 29%.
Conclusions. The scattering properties of human milk strongly depend on the homogenization method that is employed, and gentle inversion should be the preferred method. The contribution of casein micelles was relatively small for μs and g but considerably larger for μs′.
Relatively few imaging and sensing technologies are employed to study human lactation physiology. In particular, human mammary development during pregnancy as well as mammary involution after lactation have been poorly described, despite their importance for breast cancer diagnosis and treatment during these phases. Our case study shows the potential of diffuse optical spectroscopic imaging (DOSI) to uniquely study the spatiotemporal changes in mammary tissue composition during the involution of the lactating breast toward its pre-pregnant state. At nine time intervals over a period of eight months after the cessation of breastfeeding, we reconstructed 2-D maps of mammary water content, lipid content, total hemoglobin (THb) concentration, oxygen saturation (StO2), and tissue optical scattering. Mammary lipid content in the nonareolar region showed a significant relative increase of 59%, whereas water content and THb concentration showed a significant relative decrease of 50% and 48%, respectively. Significant changes were also found in StO2 and tissue optical scattering. Our findings are consistent with the gradual replacement of fibroglandular tissue by adipose tissue and vascular regression during mammary involution. Moreover, our data provide unique insight into the dynamics of breast tissue composition and demonstrate the effectiveness of DOSI as a technique to study human lactation physiology.
A decreased hemoglobin concentration (tHb) in blood (anemia) is associated with impaired oxygen delivery to organs, which can result in organ damage and heart failure. Currently, tHb analysis requires invasive methods (e.g. a fingerstick), which are time consuming and cause discomfort to the patient. Using optical spectroscopy, the tHb can be estimated by quantifying light absorption in blood. However, the accuracy of current noninvasive optical techniques for tHb quantification is limited by the background attenuation of skin and the unknown blood volume fraction in the total optical probing volume.
Spectroscopic optical coherence tomography (sOCT) allows for quantitative measurements of the optical attenuation in a confined measurement volume, potentially enabling non-invasive estimation of the hemoglobin concentration within individual blood vessels. Although multiple studies have shown that sOCT is capable of quantifying localized oxygen saturation, quantification of the tHb has not yet been reported for physiologically relevant concentrations.
With a home-built visible-light sOCT system we quantified optical attenuation in the visible wavelength range (450–600nm). Implementation of both zero-delay acquisition and focus tracking optimized system sensitivity and ensured that the measured attenuation is only affected by the attenuation of the sample itself.
We validated our method ex-vivo on human whole blood from healthy volunteers (tHb within 12-18 g/dL). The hematocrit was varied to cover the entire pathophysiological range (tHb within 9-21 g/dL) by either dilution with PBS, or plasma removal. Our system quantified the tHb in whole blood throughout the entire pathophysiological range with an accuracy of 10%.
Both Optical Coherence Tomography (OCT) and Single Fiber Reflectance Spectroscopy (SFR) are used to determine various optical properties of tissue. We developed a method combining these two techniques to measure the scattering anisotropy (g1) and γ (=1-g2/1-g1), related to the 1st and 2nd order moments of the phase function. The phase function is intimately associated with the cellular organization and ultrastructure of tissue, physical parameters that may change during disease onset and progression. Quantification of these parameters may therefore allow for improved non-invasive, in vivo discrimination between healthy and diseased tissue.
With SFR the reduced scattering coefficient and γ can be extracted from the reflectance spectrum (Kanick et al., Biomedical Optics Express 2(6), 2011). With OCT the scattering coefficient can be extracted from the signal as a function of depth (Faber et al., Optics Express 12(19), 2004). Consequently, by combining SFR and OCT measurements at the same wavelengths, the scattering anisotropy (g) can be resolved using µs’= µs*(1-g). We performed measurements on a suspension of silica spheres as a proof of principle.
The SFR model for the reflectance as a function of the reduced scattering coefficient and γ is based on semi-empirical modelling. These models feature Monte-Carlo (MC) based model constants. The validity of these constants - and thus the accuracy of the estimated parameters - depends on the phase function employed in the MC simulations. Since the phase function is not known when measuring in tissue, we will investigate the influence of assuming an incorrect phase function on the accuracy of the derived parameters.
Optical coherence tomography (OCT) has the potential to quantitatively measure optical properties of tissue such as the attenuation coefficient and backscattering coefficient. However, to obtain reliable values for strong scattering tissues, accurate consideration of the effects of multiple scattering and the nonlinear relation between the scattering coefficient and scatterer concentration (concentration-dependent scattering) is required. We present a comprehensive model for the OCT signal in which we quantitatively account for both effects, as well as our system parameters (confocal point spread function and sensitivity roll-off). We verify our model with experimental data from controlled phantoms of monodisperse silica beads (scattering coefficients between 1 and 30 mm−1 and scattering anisotropy between 0.4 and 0.9). The optical properties of the phantoms are calculated using Mie theory combined with the Percus–Yevick structure factor to account for concentration-dependent scattering. We demonstrate excellent agreement between the OCT attenuation and backscattering coefficient predicted by our model and experimentally derived values. We conclude that this model enables us to accurately model OCT-derived parameters (i.e., attenuation and backscattering coefficients) in the concentration-dependent and multiple scattering regime for spherical monodisperse samples.
Localized spectroscopic measurements of optical properties are invaluable for diagnostic applications that involve layered tissue structures, but conventional spectroscopic techniques lack exact control over the size and depth of the probed tissue volume. We show that low-coherence spectroscopy (LCS) overcomes these limitations by measuring local attenuation and absorption coefficient spectra in layered phantoms. In addition, we demonstrate the first in vivo LCS measurements of the human epidermis and dermis only. From the measured absorption in two distinct regions of the dermal microcirculation, we determine total hemoglobin concentration (3.0±0.5 g/l and 7.8±1.2 g/l) and oxygen saturation.
Knowledge of the optical properties of neonatal skin is invaluable when developing new, or improving existing optical techniques for use at the neonatal intensive care. In this article, we present in vivo measurements of the absorption μa and reduced scattering coefficient μs′ of neonatal skin between 450 and 600 nm and assess the influence of age and skin pigmentation on the optical properties. The optical properties were measured using a spatially resolved, steady state diffuse reflectance spectroscopy setup, combined with a modified spatially resolved diffusion model. The method was validated on phantoms with known values for the absorption and reduced scattering coefficient. Values of μa and μs′ were obtained from the skin at four different body locations (forehead, sternum, hand, and foot) of 60 neonates with varying gestational age, postnatal age, and skin pigmentation. We found that μa ranged from 0.02 to 1.25 mm−1 and μs′ was in the range of 1 to 2.8 mm−1 (5th to 95th percentile of the patient population), independent of body location. In contrast to previous studies, no to very weak correlation was observed between the optical properties and gestational maturity, but a strong dependency of the absorption coefficient on postnatal age was found for dark skinned patients.
Quantitative measurements of scattering properties are invaluable for optical techniques in medicine. However, noninvasive, quantitative measurements of scattering properties over a large wavelength range remain challenging. We introduce low-coherence spectroscopy as a noninvasive method to locally and simultaneously measure scattering μs and backscattering μb coefficients from 480 to 700 nm with 8 nm spectral resolution. The method is tested on media with varying scattering properties (μs = 1 to 34 mm−1 and μb = 2.10−6 to 2.10−3 mm−1), containing different sized polystyrene spheres. The results are in excellent agreement with Mie theory.
We report results of a feasibility study regarding the question whether or not venous valves can be imaged using photoacoustics, and how they will appear in the images. First an in vitro study was made on tissue phantoms consisting of blood filled rubber tubes with discontinuities in the inner tube wall. We also have studied superficial veins on the ventral side of the wrist. For excitation, an Nd:YAG laser at 1064 nm was used. Detection of acoustic signals was performed with a PVdF sensor consisting of two concentric rings. Measurements were performed on valves which where first localized by palpation. The phantom studies showed that irregular structures of the tube walls could clearly be identified from the photoacoustic images. Furthermore, in a photoacoustic image of a vein at the dorsal side of the wrist, the presence of a valve could be identified from a region of increased signal intensity within the vessel lumen.
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