title: Nonlinear ultrasound propagation through layered liquid and tissue-equivalent media: computational and experimental results at high frequency.
abstract: Nonlinear propagation has been demonstrated to have a significant impact on ultrasound imaging. An efficient computational algorithm is presented to simulate nonlinear ultrasound propagation through layered liquid and tissue-equivalent media. Results are compared with hydrophone measurements. This study was undertaken to investigate the role of nonlinear propagation in high frequency ultrasound micro-imaging. The acoustic field of a focused transducer (20 MHz centre frequency, f-number 2.5) was simulated for layered media consisting of water and tissue-mimicking phantom, for several wide-bandwidth source pulses. The simulation model accounted for the effects of diffraction, attenuation and nonlinearity, with transmission and refraction at layer boundaries. The parameter of nonlinearity, B/A, of the water and tissue-mimicking phantom were assumed to be 5.2 and 7.4, respectively. The experimentally measured phantom B/A value found using a finite-amplitude insert-substitution method was shown to be 7.4 +/- 0.6. Relative amounts of measured second and third harmonic pressures as a function of the fundamental pressures at the focus were in good agreement with simulations. Agreement within 3% was found between measurements and simulations of the beam widths of the fundamental and second harmonic signals following propagation through the tissue phantom. The results demonstrate significant nonlinear propagation effects for high frequency imaging beams.
authors.affiliation: Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, Toronto, ON, M4N 3M5, Canada. williams@sri.utoronto.ca
authors.forename: Ross
authors.initials: R
authors.lastname: Williams
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Cherin
authors.forename: Toby Y J
authors.initials: TY
authors.lastname: Lam
authors.forename: Jahangir
authors.initials: J
authors.lastname: Tavakkoli
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Zemp
authors.forename: F Stuart
authors.initials: FS
authors.lastname: Foster
mesh_terms: D003198:Computer Simulation; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008954:Models, Biological; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D012542:Scattering, Radiation; D014465:Ultrasonics; D014463:Ultrasonography / Q000379:methods*