Three-dimensional calculation of ultrasound propagation through a breast model.

Abstract

A specimen of human breast comprised mostly of fat and connective tissue was imaged with a high-resolution magnetic resonance scanner. The volume of data was segmented to construct an acoustic model by assigning values of sound speed, density, and attenuation to voxels corresponding to fat and connective tissue. Propagation of a wavefront from a point source through the model was calculated using a three-dimensional finite-difference time-domain k-space method that included perfectly matched absorbing boundary conditions to eliminate reflections at the edge of the computational domain. Because of the large 557×451×289 grid and computational demands of the three-dimensional FFT, the calculation was performed on a cluster of computers. The wave field was sampled in three orthogonal planes, one of which was offset from the origin to represent a receiving aperture. The aperture waveforms were corrected for geometry associated with the estimated location of the point source and used to calculate arrival-time and energy-level fluctuations. The root-mean-square arrival-time and energy-level fluctuations of the simulated propagation were consistent with measurements for comparable specimens of breast. The results demonstrate the feasibility of using the described combination of methods to provide insight about the way ultrasound beams are aberrated by tissue.