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

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.