Quantitative evaluation of the impact of variation of optical parameters on the estimation of blood hematocrit and oxygen saturation for dual-wavelength photoacoustics

• Subhadip Paul, Harishankar Patel, and Ratan Saha
• received 02/08/2024; accepted 04/19/2024; posted 04/22/2024; Doc. ID 521238
• Abstract: Photoacoustic (PA) spectroscopy is considered to be one of the most effective ways to measure the levelsof hematocrit (H) and oxygenation saturation (SO2) of blood, which are essential for diagnosing bloodrelated illnesses. This simulation study aims to investigate the impact of individual optical parametersi.e., optical absorption coefficient (µa), scattering coefficient (µs) and anisotropy factor (g) on the accuracyof this technique in estimating the blood properties. We first performed the Monte Carlo simulations,using realistic optical parameters, to obtain the fluence maps for various samples. The wavelengths ofthe incident light were chosen to be 532, 700, 1000 and 1064 nm. Thereafter, the k-Wave simulations wereexecuted incorporating those fluence maps to generate the PA signals. The blood properties were obtainedusing the PA signals. We introduced variations in µa, µs and g ranging from -10% to +10%, -10% to +10%and -5% to +1%, respectively at 700 and 1000 nm wavelengths. One parameter, at both wavelengths, waschanged at a time keeping others fixed. Subsequently, examined how accurately the blood parameterscould be determined at physiological hematocrit levels. A 10% variation in µa induces a 10% changein H estimation but no change in SO2 determination. Almost no change has been seen for µs variation.However, a 5% (-5% to 0%) variation in g factor resulted in approximately 160% and 115% changes in thePA signal amplitudes at 700 and 1000 nm, respectively leading to ≈ 125% error in hematocrit estimationand ≈ 14% deviation in SO2 assessment when nominal SO2 = 70% . It is clear from this study that thescattering anisotropy factor is a very sensitive parameter and its small change can result in large errors inthe PA estimation of blood properties. In future, in vitro experiments with pathological blood (inducingvariation in g parameter) will be performed and accordingly, evaluate the accuracy of the PA technique inquantifying blood H and SO2.