Objective: Red blood cell (RBC) aggregation is a unique phenomenon that occurs when red blood cells are subjected to low shear rates. Little is known about the sizes, shapes and behaviour of aggregates flowing in healthy humans. However, excessive aggregation has been shown to be an indication of pathological conditions. Therefore, characterizing RBC aggregates is important to medical research. The objective of this study was to develop a reliable technique based on image processing to assess and characterize human RBC aggregation subjected to controlled and measurable shear rates in a two-fluid flow microfluidic shearing system. Approach: Images of RBC suspensions at , and entrained by a phosphate buffered saline solution in a PDMS microchannel were captured with a high speed camera. An algorithm for processing the RBC aggregate images is presented and validated (1) on a sample of known diameter hollow glass microspheres and (2) by comparing RBC aggregate size results with those of an ImageJ image processing technique and those obtained by manual detection by two independent researchers. Main results: The proposed image processing algorithm provides a very good agreement with the manufacturer data for the glass microspheres. It also performs well on the RBC suspension images, with errors of 2–4 with respect to the manual results. Significance: The proposed automated method for RBC aggregate detection is found to be reliable and fairly accurate and will serve researchers and, perhaps in the future, clinicians to assess healthy and pathological RBC aggregation under flowing conditions.

https://iopscience.iop.org/article/10.1088/1361-6579/aaa0ad/pdf

An automated method for dynamic red blood cell aggregate detection in microfluidic flow.

Wavelets and imaging informatics: a review of the literature

The aggregation of red blood cells (RBCs) is a phenomenon that is governed by plasma fibrinogen concentration and the shear forces of flow. We propose the use of photoacoustics (PA) for the detection and characterization of RBC aggregation. A 2D simulation study was performed to investigate the dependence of the PA signal on hematocrit for non-aggregated cells and on the aggregate size for aggregated samples. Experimental confirmation of theoretical results was conducted using human RBC samples and the Imagio PA imaging device (Seno Medical Instruments Inc., San Antonio, TX). Samples were exposed to 1064 nm laser irradiation. PA signals were collected from the non-aggregated samples at varying hematocrit levels. Aggregation was induced by suspending the RBCs in various concentrations of Dextran-70. To account for the response of the imaging system, the PA spectra were calibrated by dividing by the response of the transducer measured using a needle hydrophone. Theoretical and experimental results show a monotonic increase in the PA signal amplitude with increasing hematocrit. As the size of aggregates increases, simulations demonstrate a shift towards lower frequencies in the PA power spectrum as well as enhancements as large as 11 dB compared to the non-aggregated sample. Experimental results confirm the ability of PA to detect and quantify the aggregation of RBCs. PA radiofrequency spectral analysis seems provides a quantitative means for distinguishing between aggregated and non-aggregated samples.

Characterization of red blood cell aggregation with photoacoustics: A theoretical and experimental study

The effects of aqueous extracts from the trunk bark and branches of Ceiba pentandra and from the root bark of Quassia africana Baill., which are claimed to overcome the clinical events of the sickle cell anemia (SCA) in Democratic Republic of Congo (DRC), were investigated in vitro on the red blood cells (RBC) deformity and aggregation. Blood samples from SCA patients and from healthy persons were treated with 2% sodium metabisulfite to induce hypoxia and sickling of erythrocytes, and then, were incubated with the drug extracts. It was found that extracts, used separately or together, reversed the induced deformity of RBC. On the other hand, aggregates of RBC were incubated with the plant extracts and the action was evaluated by microscope examination, which showed that cells became dispersed and isolated, while they remained stacked in the samples not treated. Sickling of RBC is a major factor among others, which are implicated for initiating the events of sickle cell crises as well as the increasing red blood cells adhesiveness observed in increased blood viscosity. These observations could support the use of the two medicinal drugs to deal with the clinical events of SCA.

	 

	Key words: Sickle cell anemia (SCA), red blood cell (RBC), deformity, hypoxia, aggregation, hemoglobin S, hemoglobin A, blood viscosity, hemolysis, Ceiba pentandra,Quassia africana Baill.

https://www.academicjournals.org/article/article1380792971_Nsimba et al.pdf

In vitro reversal of deformity and inhibition of aggregation of sickle red blood cells by two Congolese herbal medicines

In the health sector, the blood analysis is one of the most used diagnostic method. Although high technological systems provide very important information in the diagnosis of the blood diseases, a microscopic smear analysis is required for an accurate diagnosis. In this study the microscopic images of the blood cells are analysed and the location of the white blood cells are identified in the images. After this process, the determination of the kernel borders and than cell borders of the white blood cells are investigated. During this process logical and morphological operations are applied. When considering the running time of the system, the result of the investigation are satisfactory. In future studies it's expected that it will be a basis of the complex investigations such as the determination of the cancer cells or the cellular disorders.

The determination of white blood cell borders with using of logical and morphological operations in microscopic blood images

Aggregation of red blood cells which manifests in the form of rouleaux is a major determinant of flow behavior of blood in both micro and macro circulation. Any alteration in the normal behavior is found to be a critical factor in plugging of arterioles and venules forming irreversible clumps. In this work, the aggregation behavior of red blood cells is analyzed using Wavelet transforms. The artificially induced red cell aggregate images obtained from normal adult volunteers are used for the study. An arbitrary aggregation size index is derived using four different wavelet functions. The results demonstrate the ability of wavelets to precisely differentiate variations in degree of aggregation and their intercellular bonding. Also the aggregation size indices are found to be similar and consistent for a given aggregate for all wavelet functions. As the association and dissociation of red cells and the bonding strength during cluster formation are direct indicators of altered flow behavior of red cells in micro-vessels and large arteries such analysis seems to be clinically relevant. The methodology, algorithm and observations based on Wavelet transforms are discussed in detail.

/pdf/assessment-of-human-red-blood-cell-aggregation-using-image-1sh4g4302m.pdf

S. Ramakrishnan

Papers

Assessment of Human Red Blood Cell Aggregation Using Image Processing and Wavelets