Audrey Butler, Utah Valley University
High-frequency (HF) ultrasound has been shown to be sensitive to a range of breast pathologies, and is being explored for the intra-operative assessment of lumpectomy margins. This sensitivity is believed to arise from microstructure-dependent interactions of ultrasound in the tissue. The objectives of this study were to develop breast tissue phantoms with microstructures that accurately mimic the histology of normal and malignant tissue, and to determine the effects of these microstructures on HF ultrasonic spectra (10-100 MHz). Phantoms were created from a mixture of water, gelatin, and soluble fiber. To simulate various breast tissue histologies, polyethylene beads, polyethylene fibers, and nylon fibers with a range of diameters were embedded into phantoms. Microstructures ranging from randomly dispersed beads to bead-fiber constructs resembling terminal ductal lobular units (TDLUs) were modeled and tested. Pitch-catch and pulse-echo measurements were acquired using 50-MHz transducers, a HF pulser-receiver, and a 1-GHz digital oscilloscope. Spectra were derived from the data and peak densities were determined from the spectra. Peak density, which is the number of peaks and valleys in a specified spectral range, has been shown to correlate with tissue complexity. Preliminary results from dispersed beads (58-925 µm diameter) of constant volume concentration (0.8%) indicated that the smaller beads produced higher peak densities than the larger beads with a consistent and statistically significant trend. These results substantially improve upon previous phantom studies and upon results from original breast cancer studies, demonstrating the strength of the HF ultrasound response to tissue microstructure. The higher peak densities can be attributed to either the higher number of scatterers for small beads or the size of scatterer in relation to the ultrasonic wavelength. These and other results from more advanced histologically accurate microstructures modeling TDLUs will be discussed.