Effective medium model for ultrasound backscattering from aggregating red blood cells
Résumé
The Effective Medium Theory (EMT) combined with the Structure Factor Model (EMTSFM) was recently developed to model the ultrasound backscattering from aggregating Red Blood Cells (RBCs). The EMT assumes that aggregates can be treated as homogeneous effective spheres and is combined with the structure factor to consider the interaction between the effective spheres. The goal of this work was to further develop the EMTSFM and to extend its validity into a larger frequency range. The
EMT was modified to decompose the backscattering cross section of one aggregate into the coherent and incoherent components. In the previous work, only the coherent component was taken into account. The coherent component corresponds to the average wave emerging from the effective scatterer, and the incoherent component corresponds to the
uctuation of the scattering wave around its average within the effective scatterer. Virtual RBC aggregates were built in order to perform computer simulations and to produce simulated backscatter coefficients (BSCs). The BSCs computed with the new EMTSFM and with the computer simulations were compared for different aggregating conditions. The new EMTSFM
formulation is in good agreement with the computer simulations for a product of the wavenumber times the aggregate radius kRag<2.4, whereas the former EMTSFM was only valid for kRag<1.6. The mean relative error between the theoretical and simulated BSCs in the 1-50 MHz frequency bandwidth was around 19%, versus 38% with the former EMTSFM. This suggests that the new EMTSFM is an adequate model for blood characterization in high frequencies.