Biophysical Bases of Elasticity Imaging

Abstract

A mammary carcinoma and a sarcoma were grown in mice and imaged with ultrasound transducers operating with a center frequency of 20 MHz. Quantitative ultrasound (QUS) analysis was used to characterize the tumors using the bandwidth of 10 to 25 MHz. Initial QUS estimates of the scatterer properties (average scatterer diameter and acoustic concentration) did not reveal differences between the two kinds of tumors. Examination of the tumors using light microscopy indicated definite structural differences between the two kinds of tumors. In order to draw out the structural differences with ultrasound, a higher frequency probe (center frequency measured at 70 MHz) was used to interrogate the two kinds of tumors and new models were applied to the QUS analysis. QUS scatterer diameter images of the tumors were constructed using the high frequency probe. Several models for scattering were implemented to obtain estimates of scatterer properties in order to relate estimated scatterer properties to real tissue microstructure. The Anderson model for scattering from a fluid-filled sphere differentiated the two kinds of tumors but did not yield scatterer property estimates that resembled underlying structure. Using the Anderson model, the average estimated scatterer diameters were 25.5 ± 0.14 μm for the carcinoma and 57.5 ± 2.90 for the sarcoma. A new cell model was developed, which was based on scattering from a cell by incorporating the effects of the cytoskeleton and nucleus. The new cell model yielded estimates that appeared to reflect underlying structure more accurately but did not separate the two kinds of tumors. Using the new cell model, the average estimated scatterer diameters were 15.6 ± 2.2 μm for the carcinoma and 16.8 ± 3.82 μm for the sarcoma. The new cell model yielded estimates close to the actual nuclear diameter of the cell (13 μm)