Room: Davidson Ballroom B
Purpose: Methods assessing ultrasound backscatter anisotropy with array transducers have recently been developed. However, they do not provide direct information about microstructural features of specimens in question. In this work, we develop a simple geometric model of backscatter coefficient (BSC) anisotropy assessed in phantoms and in vivo human skeletal muscle.
Methods: Two phantoms were used to assess model utility: an isotropic phantom composed of spherical glass beads (75-90Î¼m diameters) and an anisotropic phantom composed of pseudo-aligned Polysulfone rods (inner diameter 200Î¼m and wall thickness 40Î¼m). The anisotropic phantom was tilted from Â±12Â° in 4Â° steps relative to the transducer aperture to determine rod orientation with our proposed model. Electronically beam steered, radiofrequency echo data were acquired for each sample and a reference phantom under the same settings with a Siemens Acuson S2000 and nominal frequency of 10MHz. The Reference Phantom Method was used to estimate BSCs within 8x8mmÂ² regions of interest. The effective scatterer diameter (ESD) was estimated from the BSC frequency dependence. Using ESD as a function of beam steering angle, a three-parameter secant model was derived dependent on minimum diameter d, fiber angle Ï†, and an anisotropy factor Ï‡ (â‰¥1 for anisotropic scatterers). As a proof of concept, these methods were applied to in vivo human rectus femoris, a highly aligned bipennate muscle.
Results: For the isotropic phantom, d was near the median of the distribution (82.3Î¼m), and Ï‡<0.5. For the anisotropic phantom and all tilt angles, d was near the inner diameter of the rods (194.3Î¼m), Ï‡>1, and Ï† was within a few degrees of the tilt angle. Results from the rectus femoris indicated d=104.9Â±2.6Î¼m, near the size of muscle fiber diameters and Ï‡>1 with Ï†=-7.9Â°.
Conclusion: Results suggest the secant model holds promise for characterizing anisotropic scatterers and for classifying normal and/or diseased human tissue.
Funding Support, Disclosures, and Conflict of Interest: Research supported by National Institutes of Health Grants T32CA009206 from the National Cancer Institute and R21HD061896, R21HD063031, and R01HD072077 from the Eunice Kennedy Shriver National Institute of Child Health and Human Development.