Olga S. Zhernovaya

The refractive index of human hemoglobin in the visible range

Because the refractive index of hemoglobin in the visible range is sensitive to the hemoglobin concentration, optical investigations of hemoglobin are important for medical diagnostics and treatment. Direct measurements of the refractive index are, however, challenging; few such measurements have previously been reported, especially in a wide wavelength range. We directly measured the refractive index of human deoxygenated and oxygenated hemoglobin for nine wavelengths between 400 and 700 nm for the hemoglobin concentrations up to 140 g l(-1). This paper analyzes the results and suggests a set of model functions to calculate the refractive index depending on the concentration. At all wavelengths, the measured values of the refractive index depended on the concentration linearly. Analyzing the slope of the lines, we determined the specific refraction increments, derived a set of model functions for the refractive index depending on the concentration, and compared our results with those available in the literature. Based on the model functions, we further calculated the refractive index at the physiological concentration within the erythrocytes of 320 g l(-1). The results can be used to calculate the refractive index in the visible range for arbitrary concentrations provided that the refractive indices depend on the concentration linearly.

Refractive index of solutions of human hemoglobin from the near-infrared to the ultraviolet range: Kramers-Kronig analysis

Abstract. Because direct measurements of the refractive index of hemoglobin over a large wavelength range are challenging, indirect methods deserve particular attention. Among them, the Kramers-Kronig relations are a powerful tool often used to derive the real part of a refractive index from its imaginary part. However, previous attempts to apply the relations to solutions of human hemoglobin have been somewhat controversial, resulting in disagreement between several studies. We show that this controversy can be resolved when careful attention is paid not only to the absorption of hemoglobin but also to the dispersion of the refractive index of the nonabsorbing solvent. We present a Kramers-Kroning analysis taking both contributions into account and compare the results with the data from several studies. Good agreement with experiments is found across the visible and parts of near-infrared and ultraviolet regions. These results reinstate the use of the Kramers-Kronig relations for hemoglobin solutions and provide an additional source of information about their refractive index.

Blood optical clearing studied by optical coherence tomography

Abstract. The main limitation of optical imaging techniques for studying biological tissues is light scattering leading to decreasing of transmittance, which lowers the imaging quality. In this case, an immersion method for optical clearing of biological tissues can provide a possible solution to this problem, because the application of biocompatible clearing agents can reduce light scattering. Optical clearing represents a promising approach to increasing the imaging depth for various techniques, for example, various spectroscopy and fluorescent methods, and optical coherence tomography (OCT). We investigate the improvement of light penetration depth in blood after application of polyethylene glycol, polypropylene glycol, propylene glycol, and hemoglobin solutions using an OCT system. Influence of clearing agents on light transport in tissues and blood was also investigated in the mouse tail vein.

Investigation of glucose-hemoglobin interaction by optical coherence tomography

In this study, the refractive index of glucose-hemoglobin solutions at different glucose concentrations was measured. Measurements were performed using Abbe refractometer at 589 nm and OCT system at 1300 nm. The different amount of glucose was added to hemoglobin solution. Theoretical values of refractive index of the glucose-hemoglobin solutions were calculated in assumption that hemoglobin and glucose molecules do not interact. The difference between the measured and calculated values of refractive index can be connected with glucose binding to hemoglobin. It is shown that the refractive index measurements can be applied to the evaluation of glycated hemoglobin amount.

Measurements of refractive index of hemoglobin mixed with glucose at physiological concentrations

This study is focused on the determination of refractive index of hemoglobin solution at different glucose concentrations using Abbe refractometer. It is shown that the changes of refractive index caused by glycation of hemoglobin may be observed using refractive index measurements. The refractive index measurements can be potentially applied for the evaluation of glycated hemoglobin amount.

Enhancement of OCT imaging by blood optical clearing in vessels – A feasibility study

Abstract Objective: The results of a feasibility study of the application of PEG-300 and fructose as two independent optical clearing agents for the reduction of light scattering in biological tissues are presented. Materials and methods: An OCT system operating at 1300 nm was used to study optical clearing effects. In in-vitro experiments in mice (n=2) an increase of the imaging depth was observed after intravenous injection of PEG-300 alone and in combination with intradermal injection of fructose. The optical clearing effect was also studied for the first time in two mice in vivo using intravenous injection of PEG-300 or solution of hemoglobin. Results: The intradermal injection of fructose in combination with the intravenous injection of PEG-300 led to a rapid optical clearing effect. In the experiments on mice in vivo the injection of PEG-300 or hemoglobin solution into the tail vein of the living mice allowed for a rapid enhancement of the vein wall and the surrounding tissue image contrast. Conclusion: The experiments on mice have clearly demonstrated that intradermal and intravenous injections of optical clearing agents enhanced light transport through the skin and blood vessels.

Study of optical clearing of blood by immersion method

Light scattering in blood caused by refractive index mismatch between erythrocyte cytoplasm and blood plasma leads to a reduction in imaging spatial resolution, imaging depth and contrast of optical imaging techniques. A possible solution to this problem is of the addition of biocompatible clearing agents, such as glucose, fructose, glycerol, dextrans etc. The basic principle of the optical clearing technique is refractive index matching between erythrocyte cytoplasm and blood plasma. Optical clearing, a technique that has been successfully demonstrated with biologic tissue, represents a promising approach to increasing the imaging depth for various techniques, for example optical coherence tomography (OCT). OCT is based on low-coherence interferometry to produce cross-sectional tomographic imaging of the internal microstructure in materials and biological tissues by measuring the echo time delay and magnitude of backscattered light. One of the main advantages of this technique is the ability to investigate turbid and highly scattering media, such as whole blood. To determine the optimal concentration of clearing agents required for blood optical clearing in order to improve light penetration depth for optical coherence tomography, clearing agents such as glucose and fructose, with various concentrations were added to blood and investigated by OCT. Changes in light attenuation and sedimentation and aggregation properties of blood depending on particular agent and its concentration were studied.

Comparable application of the OCT and Abbe refractometers for measurements of glycated hemoglobin portion in blood

It is known that glucose interacts with plasma proteins and hemoglobin in erythrocytes. Glycated (glycosylated) hemoglobin is the result of an irreversible non-enzymatic fixation of glucose on the beta chain of hemoglobin A. The amount of glycated hemoglobin depends on blood glucose concentration and reflects the mean glycemia of about the previous 2-3 months. Glycated hemoglobin is a useful marker for long-term glucose control in diabetic patients. Therefore, the search of quick and high sensitive methods for measurement of glycated hemoglobin portion in blood is important. This study is focused on the determination of refractive index of hemoglobin solution at different glucose concentrations. Measurements were performed using Abbe refractometer at 589 nm and optical coherence tomography (OCT) at 820 nm. The different amount of glucose (from 0 to 1000 mg/dl with a step 100 mg/dl) was added to hemoglobin solution. Theoretical values of refractive index of hemoglobin solutions with glucose were calculated supposing non-interacting hemoglobin and glucose molecules. There is a difference between measured and calculated values of refractive index. This difference is due to glucose binding to hemoglobin. It is shown that the refractive index measurements can be applied for the evaluation of glycated hemoglobin amount.

Errata: Blood optical clearing studied by optical coherence tomography

This article [J. Biomed. Opt.. 18, , 026014 (2013)] was originally published online on 6 February 2013 with an error in the title: the word “studied” was added. The corrected title appears above. This article was corrected online on 13 February 2013. It appears correctly in print. The Authors

REFRACTIVE INDEX OF HEMOGLOBIN AND ALBUMIN SOLUTIONS INCUBATED WITH GLUCOSE

Measurement of glycated proteins is widely used for routine monitoring of long-term glycemic status in patients with diabetes mellitus. Glycated proteins level are used both as an index of mean glycemia and as a measure of risk for development of diabetes complications. The level of glycated hemoglobin reflects the mean glycemia during the preceding 2-3 months, while glycated plasma proteins (mainly glycated albumin) reflect mean free glucose level during much more short time, about 2-3 weeks. Since glucose and glycation of proteins affect optical properties of blood, optical methods may be suggested for estimating glycated hemoglobin and glycated albumin amount in blood.