Ultrasonic backscatter coefficient quantitative estimates from Chinese hamster ovary and BALB/3T3 cell pellet biophantoms
In this study a cell pellet biophantom technique is introduced and applied to the ultrasonic backscatter coefficient (BSC) estimate using Chinese hamster ovary (CHO), and new and old 3T3 cells. Also introduced, for its geometrical similarities to eukaryotic cells, is a concentric sphere scattering model. BSC estimates from cell pellet biophantoms of known number density were performed with 20, 40 and 80 MHz focused transducers (overall bandwidth: 20-100 MHz). These biophantoms were histologically processed and then evaluated for cell viability. For low cell concentrations, cell pellet BSC estimates were in agreement with the concentric sphere model. Fitting the model to the BSC data yielded quantitative values for the outer sphere and inner sphere. The concentric sphere model thus appears suitable as a tool for providing quantitative information on cell structures and will tend to have a fundamental role in the classification of biological tissues. For high cell concentrations, the cells are close to each other so that the scattering becomes more complicated. The magnitude and shape of the BSC versus frequency curve, and consequently the parameter estimates from the concentric sphere model, are all affected by the high-concentration effect when the volume density reaches 30%. At low frequencies (ka<1), the effect tends to decrease BSC, as is also observed by other researchers. However, what is new in our findings is that the effect could either increase or decrease BSC at frequencies beyond the Rayleigh region. The concentric sphere model least-squares estimates show a decrease in cell radius with number density (15.8, 14.6, 15.1, 13.6, 9.6, 7.1 μm for 1.25, 4.97, 19.7, 72.3, 224, 473 Mcells/mL CHO cell pellets respectively, and 11.4, 9.1 10.7, 8.4 μm for 1.24, 4.84, 17.7, 52.3 Mcell/mL new 3T3 cell pellets, respectively), which indicates that the concentric spheres model starts to break up at large cell concentrations. The critical volume density, starting from when the model becomes inapplicable, is estimated to be between 10% and 30%.
Quantitative Ultrasound, Ultrasonic Backscatter Coefficient, Biological Phantom, Concentric Sphere Model, High Concentration
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign