Structure-factor model for quantifying the ultrasound scattering from concentrated cell pellet biophantoms
Résumé
Ultrasonic backscatter coefficient (BSC) measurements were performed on K562 cell pellet
biophantoms with cell concentrations ranging from 0.6% to 30% using ultrasound in the 10-42MHz frequency band.
The concentrated biophantoms mimic densely packed cells with known concentrations and are thus simplified
versions of real tumor. Three scattering models, the fluid-filled-sphere model (FFSM), the Gaussian model (GM), and
the structure factor model (SFM), were compared for modeling the scattering of the biophantoms. The GM and FFSM
assume sparse, independently, and randomly distributed scatterers and are thus suitable for modelling dilute media;
however, the SFM does not contain these assumptions and therefore can model dense media accurately. First, a
parameter-estimation procedure was developed to estimate scatterer size and acoustic impedance contrast
(assuming that cell concentrations were known a priori) and thereby compare theoretical with measured BSCs for all
studied concentrations. The SFM yielded scatterer-radius estimates of 6.4 μm, which were consistent with the cell
radius measured by optical microscopy. Second, the ability of the three models to estimate the scatterer size and
acoustic concentration was compared. These scatterer properties were predicted well by the SFM, whereas the GM
and the FFSM underestimated cell size and overestimated acoustic concentration for the more-concentrated
biophantoms.