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3EFFICACY OF RADIOPAQUE SUBSTANCES IN OPTICAL CLEARING AND THEIR IMPACT ON
RED BLOOD CELL AGGREGATION
P A. MOLDON1. M.K. MAKSIMOV1, YU.I. SURKOV2, A.E. LUGOVTSOV1, P A. TIMOSHINA2,
PENGCHENG LI3. A.V. PRIEZZHEVi
'Faculty of Physics, Lomonosov Moscow State University, Moscow, Russia 2Research-Educational Institute of Optics and Biophotonics, Saratov State University, Saratov, Russia Huazhong University of Science and Technology, Huazhong, China
INTRODUCTION
To increase the depth of penetration of visible and near-infrared radiation into the biological tissues for enhancement the efficacy of diagnostic and therapeutic procedures. numerous techniques are used. For example. to increase the image contrast the optical clearing technique is used [1]. Typically. optical clearing agents (OCAs) are used for this purpose. The mechanism of the OCA action is based on the reduction of the reflectance from the tissue surface and diffuse penetration of the OCA into the deep layers of tissues. The second process results in the decreasing of multiple light scattering by equalizing the relative refractive index of the light scattering inhomogeneities inside the investigated tissue. These makes the tissues optically more homogeneous. which results in the increase of the depth and resolution of imaging techniques. for example the digital capillaroscopy method for in vivo visualization of terminal capillaries in the nail bed area [2]. One of the aims of this work was to study the efficacy of various OCAs which are already used in clinical practice as radiopaque substances for improving the optical visualization of subcutaneous structures (in particular. nail bed capillaries) in vivo. The measurements were performed within the nail bed using optical coherence tomography (OCT). Another goal of this work was to investigate the effect of these OCA on the aggregation properties of rat's red blood cells (RBCs) to study the mechanisms of OCAs affecting the blood flow. To study this effect in vitro laser aggregometry method was used.
MATHERIALS AND METHODS
In this work seven different OCAs. including magnevist. gadovist. visipaque. mixture of visipaque and DMSO (90% and 10%. correspondingly). mixture of visipaque and polypropylene glycol 400 (40% and 60%. correspondingly). accupaque and a solution consisting of visipaque 54%. DMSO 10%. polypropylene glycol 36% were used. Each OCA was applied to the nail beds of 6 healthy volunteers. The OCT measurements were performed before the surface application of OCA on the nail bel area. right after and further each 5 minutes till 15 minutes. To prevent drying out of OCAs a special tissue applicator moistened with certain OCA was placed on the nail bed area. Each sample was imaged using a high-resolution OCT GAN930V2-BU (Thorlabs. USA) with wavelength 930±5 nm [2]. The results were evaluated based on the changes in the attenuation coefficient calculated from the OCT B - scan images obtained.
The blood for the laser aggregometry in vitro experiments was drawn from the heart of healthy rats. To measure the effect of magnevist and gadovist on RBCs aggregation properties samples with OCA concentrations of 1%. 5% and 10% were prepared. All samples were prepared by mixing the whole blood with OCA in the particular concentration. As a control samples. saline samples were prepared in the same concentrations in order to differentiate the direct effect of OCA and the effect of blood dilution resulting in reducing the concentration of proagregant macromolecules in blood. Each sample was measured with a laser aggregometer of RBCs - RheoScan (RheoMeditech. Republic of Korea) [3.4]. This device allows to measure the microrheological parameters of blood in vitro using disposable cuvettes. There is a metal bar inside each cuvette which starts to rotate and disperse all aggregates inside the sample the beginning of the measurements. Then the bar stops. and the process of spontaneous aggregation starts and devise register the time dependency of the intensity of light. scattered forward by the blood sample. By this method aggregation index (AI) was measured for each sample. It is calculated as the ratio between the area under the aggregation curve and the whole area below and above the curve during the first 10 seconds of spontaneous aggregation process.
RESULTS
Figures 1 represents the normalized attenuation coefficient calculated for different depths of the nail bed area, OCAs and time. The effect of optical clearing was demonstrated. Thus, the attenuation coefficient decreases for both chosen depths, however, for the depth of 0 - 50 ^m the decrease is stronger. Three component (3Component) and visipaque - PG solutions showed the greatest efficiency for the optical clearing for the depth of 0 - 50 ^m, the decrease of the attenuation coefficient is 31% and 30% respectively after 15 minutes since the OCA application.
Figure 1: Dependence of the attenuation coefficient on time under application for various OCAs for the depths 0-50 ¡m (left), 100 - 200 ¡m (right). VisDMSO - visipaque and DMSO (90% and 10%, correspondingly), VisPG40 - mixture of visipaque and polypropylene glycol 400 (40% and 60%, correspondingly), 3Component - a solution consisting of visipaque 54%, DMSO 10%, polypropylene glycol 36%.
For the depth in the region of 100 - 200 ^m the effect of OCAs is less noticeable, for the same OCA coefficient decreases only by 17% and 6% respectively.
Figure 2: Dependence of the AI on concentrations of OCA and saline solution. Wb - gadovist, m - magnevist, f - saline solution. Numbers 1 - 10 concentrations in %.
whole blood, g
Figure 2 shows that AI parameter decreases for all OCAs and saline solution. The decrease is 64 ± 10%, 59 ± 7% and 42 ± 13% respectively for gadovist, magnevist and saline solution for their incubation with blood samples in concentration of 10%.
CONCLUSION
Obtained results shows, that the selected radiopaque agents can be used for the optical clearing of the tissues of the human nail bed to depths of about 50 ^m. It means they can be used for the visualization of the nail bed capillaries in capillaroscopy method [5]. The most effective OCAs for the enhancement of light penetration into the tissue were a solution consisting of visipaque 54%, DMSO 10%, polypropylene glycol 36%. Also, it was shown, that the studied agents have no pronounced effect on the aggregation of RBCs, since the decrease in aggregation with an increase in the OCA concentration is the same as for a sample with a saline solution. This decrease may be caused by blood dilution and a decrease in hematocrit.
ACKNOWLEDGMENTS
All experiments, blood supply and data analysis were supported by the Russian Science Foundation Grant No. 23-45-00027.
REFERENCES
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