title: Enhancement of subharmonic emission from encapsulated microbubbles by using a chirp excitation technique.
abstract: Subharmonic contrast imaging promises to improve ultrasound-imaging quality by taking advantage of an increased contrast to tissue signal. However, acoustic pressures beyond the subharmonic generation threshold using common ultrasound pulses may induce significant contrast microbubble destruction. In this work, a chirp excitation technique is presented to enhance the subharmonic emission from encapsulated microbubbles. Chirp signals with a center frequency of 5 MHz, variable frequency range and duration time are employed to drive microbubbles in numerical simulation and experimental studies. We provide a theoretical evaluation of the chirp excitation pressure threshold and the acoustic pressure dependence of subharmonic based on Church's model and demonstrate that the amplitude and axial resolution of the subharmonic can be optimized by proper selection of the frequency range and time duration of the chirp signal. Measurements are qualitatively in agreement with the simulation. Moreover, we demonstrate that chirp excitation may be able to improve the amplitude of the subharmonic component up to 22 dB over the pulse excitation. The chirp excitation technique could potentially be used for improving the subharmonic contrast imaging quality.
authors.affiliation: Institute of Acoustics, Key Lab of Modern Acoustics, Nanjing University, Nanjing 210093, People's Republic of China. dzhang@nju.edu.cn
authors.forename: Dong
authors.initials: D
authors.lastname: Zhang
authors.forename: Yanjun
authors.initials: Y
authors.lastname: Gong
authors.forename: Xiufen
authors.initials: X
authors.lastname: Gong
authors.forename: Zheng
authors.initials: Z
authors.lastname: Liu
authors.forename: Kaibin
authors.initials: K
authors.lastname: Tan
authors.forename: Hairong
authors.initials: H
authors.lastname: Zheng
mesh_terms: D000465:Algorithms; D003287:Contrast Media; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D045423:Microbubbles; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014463:Ultrasonography / Q000295:instrumentation / Q000379:methods*