Effects of erythrocyte oxygenation on optoacoustic signals

Ratan K Saha,Michael C Kolios

doi:10.1117/1.3655355

Abstract

A theoretical model examining the effects of erythrocyte oxygenation on optoacoustic (OA) signals is presented. Each erythrocyte is considered as a fluid sphere and its optical absorption is defined by its oxygen saturation state. The OA field generated by a cell is computed by solving the wave equation in the frequency domain with appropriate boundary conditions. The resultant field from many cells is simulated by summing the pressure waves emitted by individual cells. A Monte Carlo algorithm generates 2-D spatially random distributions of oxygenated and deoxygenated erythrocytes. Oxygen saturation levels of oxygenated cells a assumed to be 100% and 0% for deoxygenated cells. The OA signal amplitude decreases monotonically for the 700-nm laser source and increases monotonically for 1000 nm optical radiation when blood oxygen saturation varies from 0 to 100%. An approximately sixfold decrease and fivefold increase of the OA signal amplitude were computed at those wavelengths, respectively. The OA spectral power in the low-frequency range (<10 MHz) and in the very high-frequency range (>100 MHz) decreases for 700 nm and increases for 1000 nm with increasing blood oxygen saturation. This model provides a theoretical framework to study the erythrocyte oxygenation-dependent OA signals.

Highlights

Accurate estimation of blood oxygenation is of great importance in making critical decisions associated with clinical situations
The OA amplitude is maximum at SO2 = 0%, where the sample contains only RBCDs
It is minimum at SO2 = 100% because constituent cells are only RBCOs

Summary

Introduction

Accurate estimation of blood oxygenation is of great importance in making critical decisions associated with clinical situations. Blood oxygen level can be monitored noninvasively by using a near-infrared spectroscopy method. It is a very convenient method and uses translucent body parts (e.g., earlobes, fingertips, etc.) to determine the blood oxygen saturation.[1] the major limitations of this technique are the (i) small penetration depth due to strong light scattering and (ii) the inability to distinguish between venous and arterial blood due to poor spatial resolution. The optoacoustic (OA) technique promises to provide a real-time, noninvasive blood oxygenation monitoring method by overcoming these drawbacks and is expected to be useful for the assessment of oxygenation in many sites of physiological interest, including the brain.[2] Note that the brain is very sensitively dependent on oxygen for its normal function, and accurate quantification of the brain tissue oxygenation can play a crucial role for treating patients with traumatic brain injury or neurophysiological disorders.[1]

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