Grant: Travel Awards - Institute Community Support

Photoacoustic (PA) imaging of blood flow can provide a label free and noninvasive assessment of the oxygen saturation (sO2). Flow induced red blood cell (RBC) aggregation are typically not considered in sO2 estimations even though RBC aggregates modify O2 release. In this work, the PA images were reconstructed for each temporal frame during the simulated blood flow, and compared to in vivo PA images of the RA. A particle based model was constructed using the Doppler velocity of pulsatile blood flow recorded from the RA. The positions of randomly distributed, identical spherical RBCs in the lateral axial plane (20 mm × 2 mm) were traced at each time step. The cells in the left hand side (LHS) from 0 mm moved toward the right hand side (RHS), based on the parabolic velocity profile in the axial position. When the cells flowing from the LHS overlapped the cells positioned to its right, the overlapped cells were considered a single spherical aggregate. At each step, the time dependent PA amplitude (PAamp) from each cell (or aggregate) was computed by modeling and accounting for the directivity of a 21 MHz (9.2 ~ 32.8 MHz bandwidth) linear array. PA images of the RA were acquired using the VevoLAZR equipped with a 21 MHz linear array probe and compared to the developed model. The PAamp on the parabolic front was larger due to RBC aggregates (larger absorber). The spatiotemporal distribution of the measured PAamp was reconstructed in the same way. The overall trend was similar in both cases. Specifically, the PAamp at the LHS was 10 dB smaller than the one at the RHS, suggesting that the simulated aggregation kinetics occur in vivo. These results can be used to study the in silico, label free, noninvasive assessment of the spatiotemporal distribution of sO2 in vivo. Furthermore, the improved particle model can provide insights into the effect of RBC aggregation on PA wave generation during in vivo blood flow measurements.