Abstract

The frequency domain optoacoustic (OA) wave equation is inherently inhomogeneous. The first inho-mogeneous term arises because of the OA effect (i.e., conversion of optical energy into acoustical energy). The second term appears due to sound-speed mismatch between the source and the ambient medium. The conventional Green’s function method works well in absence of the second term (i.e., acoustically homoge-neous source). Recently, it has been shown that a modified Green’s function (MGF) approach provides faithful solution to the OA wave equation for an acoustically inhomogeneous source. Herein, we employ the MGF technique for accurate estimation of the OA spectra for normal and pathological red blood cells (RBCs). The shapes in 2D mimicking normal RBC, stomatocyte and echinocyte (with six equidistant identical spicules) were simulated (with constant area ≈ 16.5 µm²) and subsequently, the OA spectra were computed over 10-1000 MHz by evaluating the integral equation employing the Monte Carlo integration method. The OA spec-trum for an equivalent disc was also calculated for comparison. The sound-speed within the source region was taken as 1639 m/s and that of the surrounding medium was chosen as 1500 m/s. The first minimum of the OA spectra for disc and echinocyte appeared almost at the same location (440 MHz) when probed from an angle, θ=π/4 with respect to the axis of symmetry. The locations for the first minimum became 280 and 390 MHz, respectively for normal RBC and stomatocyte (for θ=π/4). These 0A spectral features may be useful for morphological characterization of normal and deformed RBCs.

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