Validation of the Effective Medium Theory combined with the Structure Factor Model in predicting RBCs aggregation from the ultrasonic backscattering coefficient: Ali Traoré-Dubuis 1 E. Franceschini 2 , R.K. Saha 3 , G. Cloutier 1,4 1 Laboratory of Biorheology and Medical Ultrasonics, Research Center, University of Montreal Hospital, Notre-Dame Hospital,Montreal Canada 2 Laboratory of Mechanics and Acoustics, LMA - CNRS UPR 7051, Marseille, France 3 Department of Physics, Ryerson University, Toronto, Ontario, Canada 4 Department of Radiology, Radio-Oncology and Nuclear Medicine, University of Montreal, Montreal, Canada Abstract Quantitative ultrasound based on backscattering coefficient applied to blood aim to characterize RBCs (RBCs) aggregation, a biophysical phenomenon associated with hemorheological disorders. Mathematical modeling is known to be the optimal way to describe the interaction between ultrasound and tissues occurring at the cellular level. The structure factor model (SFM), considered as the exact scattering model, predicted the backscattering coefficient from blood. However, the numerical SFM cannot be applied in real time for practical measurements and does not provide structural parameter such as aggregate size to assess the level of aggregation. Therefore, a new model based on the effective medium theory was proposed in order to tackle this difficulty. The effective medium theory combined with the structure factor model (EMTSFM) can be applied in real time and contrary to the SFM provides two indices of the aggregate state in vivo: the aggregate size and compactness. Our aim here is to assess the accuracy of the EMTSFM against the SFM by comparing their BSC in the framework of a forward problem, i.e., the