title: Difference frequency and its harmonic emitted by microbubbles under dual frequency excitation.
abstract: Vibro-acoustography is an elasticity imaging method that uses two ultrasound beams of slightly different frequency to excite an object and detects the resulting acoustic emission (AE) at the difference frequency. This method is especially sensitive to bubbles due to their nonlinearity. This study explores the harmonic acoustic emission (HAE) at twice the difference frequency emitted from bubbles. A perturbation method based on the dynamic bubble equation is used to derive the AE and HAE from a single bubble excited by dual frequency waves. Simulation shows that HAE is generated only by microbubbles whose resonant frequencies match the incident ultrasound frequencies. In contrast, AE is more sensitive to resonance at the difference frequency, which is relevant to sub-millimeter bubbles. This finding was confirmed by experiments where HAE was produced from Optison microbubbles, but not from larger air bubbles which are off resonance at the incident ultrasound frequency. In conclusion, harmonic acoustic emission is present for microbubbles. It is very sensitive to the size of the bubble and may be used for selective detection of microbubbles.
authors.affiliation: Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, 200 First ST. SW., Rochester, MN 55905, USA. chen.shigao@mayo.edu <chen.shigao@mayo.edu>
authors.forename: Shigao
authors.initials: S
authors.lastname: Chen
authors.forename: Randall
authors.initials: R
authors.lastname: Kinnick
authors.forename: James F
authors.initials: JF
authors.lastname: Greenleaf
authors.forename: Mostafa
authors.initials: M
authors.lastname: Fatemi
mesh_terms: D000418:Albumins / Q000737:chemistry* / Q000528:radiation effects*; D003198:Computer Simulation; D004307:Dose-Response Relationship, Radiation; D005466:Fluorocarbons / Q000737:chemistry* / Q000528:radiation effects*; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D045423:Microbubbles; D008956:Models, Chemical; D011829:Radiation Dosage; D014463:Ultrasonography / Q000379:methods*
chemical_list: D000418:Albumins; C099458:FS 069; D005466:Fluorocarbons