Analysis of human fibroadenomas using three-dimensional impedance maps

Three-dimensional impedance maps (3DZMs) are virtual volumes of acoustic impedance values constructed from histology to represent tissue microstructure acoustically. From the 3DZM, estimations can be made for ultrasonic backscatter and scatterer properties, such as effective scatterer diameter (ESD). Additionally, the 3DZM can be exploited to visualize and identify possible scattering sites, which may aid in the development of more effective scattering models to better represent the ultrasonic interaction with underlying tissue microstructure. In this study, 3DZMs were created from several human fibroadenoma samples. ESD estimates were obtained using the fluid-filled sphere form factor model. These estimates were made using two regions of interest (ROIs) sizes: cubes of side length 300 µm and 150 µm. This estimation technique allowed a better understanding of the spatial distribution and variability of the estimates throughout the volume. For a collection of 33 3DZMs, the ESD was estimated to be 99±43 µm with the large ROI and 65±30 µm when using the small ROI. The 3DZMs were then investigated visually to identify possible scattering sources, which conformed to the estimated characteristic scatterer dimensions. This visualization and comparison resulted in the identification of possible ultrasonic scattering sources within human fibroadenomas.