Reconstruction of tissue scatter characteristics using 3D ultrasound tomography

Abstract

Conventional reflectivity imaging with Ultrasound Tomography (USCT) reconstructs qualitative images proportional to the magnitude of the impedance gradient. We propose a method to additionally recover the scatter characteristics for each reconstructed voxel, i.e. whether a reflection is diffuse or specular. This is achieved using a modification of 3D Synthetic Aperture Focusing Technique (SAFT). Our novel approach separates the incoming and outgoing ultrasound intensity in each voxel according to the incident direction and the direction to the receiver. To reduce memory requirements, we propose several strategies for selecting a subset of data or aggregating data to predefined directions. The reconstruction leads to five-dimensional data, from which for each voxel in 3D space, a 2D scatter map can be derived. It can be interpreted as the distribution of energy which has been introduced from a certain direction and which has been reflected into a particular direction. We validated our approach by a simulation based on the Phong reflection model and perform first reconstructions of experimental data. Using the 2D scatter maps it is possible to distinguish specular from diffuse reflections visually. Extracting first-order statistics from the 2D scatter maps for each voxel can be a means to break down the 5D information to 3D for traditional slice-based visualization. The multidimensional data provided by our method may be used in future as a biomarker for diagnosis as e.g. a plain surface of a cyst may reflect the ultrasound differently than a rough surface of a spiculated mass.