title: Toric focusing for radiation force applications using a toric lens coupled to a spherically focused transducer.
abstract: Dynamic elastography using radiation force requires that an ultrasound field be focused during hundreds of microseconds at a pressure of several megapascals. Here, we address the importance of the focal geometry. Although there is usually no control of the elevational focal width in generating a tissue mechanical response, we propose a tunable approach to adapt the focus geometry that can significantly improve radiation force efficiency. Several thin, in-house-made polydimethylsiloxane lenses were designed to modify the focal spot of a spherical transducer. They exhibited low absorption and the focal spot widths were extended up to 8-fold in the elevation direction. Radiation force experiments demonstrated an 8-fold increase in tissue displacements using the same pressure level in a tissue-mimicking phantom with a similar shear wave spectrum, meaning it does not affect elastography resolution. Our results demonstrate that larger tissue responses can be obtained for a given pressure level, or that similar response can be reached at a much lower mechanical index (MI). We envision that this work will impact 3-D elastography using 2-D phased arrays, where such shaping can be achieved electronically with the potential for adaptive optimization.
authors.forename: Bastien
authors.initials: B
authors.lastname: Arnal
authors.forename: Thu-Mai
authors.initials: TM
authors.lastname: Nguyen
authors.forename: Matthew
authors.initials: M
authors.lastname: O'Donnell
mesh_terms: D003198:Computer Simulation; D054459:Elasticity Imaging Techniques / Q000295:instrumentation*; D007909:Lenses; D019047:Phantoms, Imaging; D014159:Transducers