Quantitative Ultrasound Assessment of Red Blood Cell Aggregation Alongside Photoacoustic-Based Oxygen Saturation in the Human Radial Artery

Our group has demonstrated that photoacoustic (PA) imaging can assess oxygen saturation (SO2) associated with red blood cell (RBC) aggregation (Bok et al., JBO, 2021). In this work, we further investigate how the RBC aggregation quantitatively impacts the in vivo assessment of the SO2 in the radial artery of healthy volunteers by using structure factor size estimation based on ultrasound (US) imaging. Human US images were acquired simultaneously with PA images using a 21 MHz probe in the VevoLAZR imaging system (Fujifilm-VisualSonics). The range of the optical wavelength of illumination was 700 nm - 900 nm. The aggregate diameter was computed by the US-based structure factor size estimation. The sO 2 of the radial artery was computed by linear spectral unmixing. The effects of RBC aggregation on the sO 2 were investigated using the US-based structure factor size estimation. The experimental results were grouped by age, such as the 20s, 30s, and 40s. The US power (Pus) is largest during the diastole (P US-max ) and smallest during the systole (P US-min ). The difference between P US-max and P US-min increased with age, i.e., 1.7 dB, 2.1 dB, and 2.7 dB for the 20s, 30s, and 40s, respectively. The aggregate diameter increased with volunteer age. Older individuals have been shown to have a larger change in the RBC aggregate diameter during a pulsatile cycle, potentially altering the oxygen delivery to surrounding tissues. This study aims to establish fundamental relationships between the sO 2 and hemodynamic blood flow behavior, thus facilitating the clinical translation of this promising technology.