title: Bubble-based acoustic radiation force elasticity imaging.
abstract: Acoustic radiation force is applied to bubbles generated by laser-induced optical breakdown (LIOB) to study viscoelastic properties of the surrounding medium. In this investigation, femtosecond laser pulses are focused in the volume of gelatin phantoms of different concentrations to form bubbles. A two-element confocal ultrasonic transducer generates acoustic radiation force on individual bubbles while monitoring their displacement within a viscoelastic medium. Tone burst pushes of varying duration have been applied by the outer element at 1.5 MHz. The inner element receives pulse-echo recordings at 7.44 MHz before, during, and after the excitation bursts, and crosscorrelation processing is performed offline to monitor bubble position. Maximum bubble displacements are inversely related to the Young's moduli for different gel phantoms, with a maximum bubble displacement of over 200 microm in a gel phantom with a Young's modulus of 1.7 kPa. Bubble displacements scale with the applied acoustic radiation force and displacements can be normalized to correct for differences in bubble size. Exponential time constants for bubble displacement curves are independent of bubble radius and follow a decreasing trend with the Young's modulus of the surrounding medium. These results demonstrate the potential for bubble-based acoustic radiation force methods to measure tissue viscoelastic properties.
authors.affiliation: Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109-2099, USA. terpeldi@umich.edu
authors.forename: Todd N
authors.initials: TN
authors.lastname: Erpelding
authors.forename: Kyle W
authors.initials: KW
authors.lastname: Hollman
authors.forename: Matthew
authors.initials: M
authors.lastname: O'Donnell
mesh_terms: D003198:Computer Simulation; D003287:Contrast Media; D004548:Elasticity; D005740:Gases / Q000032:analysis / Q000737:chemistry*; D005782:Gels / Q000032:analysis / Q000737:chemistry*; D007089:Image Enhancement / Q000379:methods*; D007834:Lasers; D045423:Microbubbles; D033401:Microscopy, Acoustic / Q000295:instrumentation / Q000379:methods*; D008954:Models, Biological; D019047:Phantoms, Imaging; D013314:Stress, Mechanical
chemical_list: D003287:Contrast Media; D005740:Gases; D005782:Gels