In vitro photoacoustic spectroscopy of pulsatile blood flow: Probing the interrelationship between red blood cell aggregation and oxygen saturation

Abstract

We investigate the optical wavelength dependence in quantitative photoacoustic (QPA) assessment of red blood cell (RBC) aggregation and oxygen saturation (sO ) during pulsatile blood flow. Experimentally, the pulsatile flow was imaged with a 700 to 900 nm laser using the VevoLAZR. Theoretically, the photoacoustic (PA) signals were computed based on a Green's function integrated with a Monte Carlo simulation of radiant fluence. The pulsatile flow created periodic conditions of RBC aggregation/nonaggregation, altering the aggregate size, and, in turn, the sO . The dynamic range, DR (a metric of change in PA power) from 700 to 900 nm for nonaggregated RBCs, was 5 dB for both experiment and theory. A significant difference in the DR for aggregated RBCs was 1.5 dB between experiment and theory. Comparing the DR at different wavelengths, the DR from nonaggregated to aggregated RBCs at 700 nm was significantly smaller than that at 900 nm for both experiment (4.0 dB < 7.1 dB) and theory (5.3 dB < 9.0 dB). These results demonstrate that RBC aggregation simultaneously affects the absorber size and the absorption coefficient in photoacoustic imaging (PAI) of pulsatile blood flow. This investigation elucidates how QPA spectroscopy can be used for probing hemodynamics and oxygen transport by PAI of blood flow.

Imaging of human peripheral blood vessels during cuff occlusion with a compact LED-based photoacoustic and ultrasound system

“…The observed periodicity of the PA signal from the digital artery could arise from several factors, and further study is needed to provide a full explanation. A recent study by Bok et al pointed to the effects of aggregation/non-aggregation of red blood cells throughout the cardiac cycle on PA signal amplitudes and wavelength-dependencies [12].…”

Feasibility of photoacoustic imaging for the non‐invasive quality management of stored blood bags

“…Novel optical approaches such as the spatially offset Raman spectroscopy and the diffuse reflectance spectroscopy technique have shown potential for non‐invasive acquisition of RCC parameters during storage. PA imaging is a promising modality which has shown potential to obtain functional (oxygenation) and morphological (shape/size) information of biological absorbers . Hand‐held PA imaging probes like the ones used in this study are becoming commercially available and allow for imaging versatility in clinical and laboratory environments.…”

“…Over the last decade, photoacoustic (PA) technologies have made significant strides at exploiting the optical window for non‐invasive imaging . PA technologies excite chromophores with short‐pulsed (<10 ns) lasers to obtain both morphological and functional information related to the chromophore absorbing the incident light, the latter achieved by sweeping the wavelength of illuminations . Unlike conventional absorption or reflectance techniques , PA imaging detects ultrasonic waves whose scattering in tissue is typically several orders of magnitude lower than electromagnetic radiation.…”

Photoacoustic simulations of microvascular bleeding: spectral analysis and its application for monitoring vascular-targeted treatments

“…Changes in the frequency content of the PA signals are associated with the size, concentration, and spatial distribution of dominant optical absorbing chromophores. [13][14][15] This is analogous to quantitative ultrasound analysis, which is associated with the dominant ultrasound scattering source. 16,17 PA spectral analysis provides system-independent parameters that are correlated to the structure of optically absorbing chromophores.…”