title: Displacement analysis of diagnostic ultrasound backscatter: a methodology for characterizing, modeling, and monitoring high intensity focused ultrasound therapy.
abstract: Accurate monitoring of high intensity focused ultrasound (HIFU) therapy is critical for widespread clinical use. Pulse-echo diagnostic ultrasound (DU) is known to exhibit temperature sensitivity through relative changes in time-of-flight between two sets of radio frequency (RF) backscatter measurements, one acquired before and one after therapy. These relative displacements, combined with knowledge of the exposure protocol, material properties, heat transfer, and measurement noise statistics, provide a natural framework for estimating the administered heating, and thereby therapy. The proposed method, termed displacement analysis, identifies the relative displacements using linearly independent displacement patterns, or modes, each induced by a particular time-varying heating applied during the exposure interval. These heating modes are themselves linearly independent. This relationship implies that a linear combination of displacement modes aligning the DU measurements is the response to an identical linear combination of heating modes, providing the heating estimate. Furthermore, the accuracy of coefficient estimates in this approximation is determined a priori, characterizing heating, thermal dose, and temperature estimates for any given protocol. Predicted performance is validated using simulations and experiments in alginate gel phantoms. Evidence for a spatially distributed interaction between temperature and time-of-flight changes is presented.
authors.affiliation: Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Seattle, Washington 98105, USA. gavriel@u.washington.edu
authors.forename: Gavriel
authors.initials: G
authors.lastname: Speyer
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Kaczkowski
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Brayman
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Crum
mesh_terms: D000464:Alginates / Q000737:chemistry; D003198:Computer Simulation; D005782:Gels; D019220:High-Energy Shock Waves; D057086:High-Intensity Focused Ultrasound Ablation / Q000295:instrumentation; D016014:Linear Models; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D013696:Temperature; D013814:Thermal Conductivity; D013997:Time Factors; D014159:Transducers; D014463:Ultrasonography / Q000295:instrumentation
chemical_list: D000464:Alginates; D005782:Gels