Author: Alexandra Christensen, Timothy J. Hall, Ivan M. Rosado-Mendez 👨🔬
Affiliation: University of Wisconsin, Madison, Departments of Medical Physics and Radiology, University of Wisconsin-Madison 🌍
Purpose: Quantitative ultrasound techniques based on the statistical analysis of speckle are currently being deployed commercially and clinically as sources of biomarkers associated with tissue microstructure. However, current understanding of the link between speckle statistics and microstructure assumes point-like, isotropic sources of scattering, thus ignoring important fibrous tissue components like muscle and nerve fibers or collagen bundles in cancer microenvironment. The purpose of this study is to create a phantom that simulates collections of anisotropically-scattering tissue components to investigate the relationships between fibrous tissue microstructure and quantitative ultrasound biomarkers based on first-order speckle statistics.
Methods: Phantoms were constructed from merino wool roving (22-micron diameter) and attached to a calibrated spring so that a repeatable degree of fiber alignment could be induced by applying a known tension. Phantoms were imaged with a Siemens Sequoia ultrasound scanner, steering the acoustic beams at -10, -5, 0, 5, and 10 degrees relative to the fiber orientation to investigate scattering anisotropy. Parameters of the Nakagami and homodyned K speckle statistics models were calculated from each steered acquisition in the proposed phantoms.
Results: Variations in wool fiber alignment in the phantom resulted in statistically significant differences in the variation of speckle statistics features with steering angle: 35% in Nakagami m, 151% in Homodyned K alpha and 23% in Homodyned K k. These changes were not observed in phantoms with isotropic scatterers.
Conclusion: This study presents a novel method for constructing phantoms to investigate sub-resolution anisotropic scattering with diagnostic ultrasound. The results of this study suggest that changes in speckle statistics parameters with respect to steering angle can be used to measure the degree of alignment of anisotropic acoustic scatterers separately from spatial density. These phantoms can help validate the clinical value of quantitative ultrasound biomarkers based on speckle statistics as a bridge to complex tissue microstructure.