Passive cavitation imaging of echogenic liposomes

Previously, passive cavitation imaging has been described in the context of continuous-wave high-intensity focused ultrasound thermal ablation. However, the technique has potential use as a feedback mechanism for pulsed-wave therapies, such as ultrasound-mediated drug delivery. In this paper, results of experiments and simulations are reported to demonstrate the feasibility of passive cavitation imaging using pulsed ultrasound insonations and how the images depend on pulsed ultrasound parameters. The passive cavitation images were formed from channel data that was beamformed in the frequency domain. Experiments were performed in an invitro flow phantom with an experimental echo contrast agent, echogenic liposomes, as cavitation nuclei. It was found that the pulse duration and envelope have minimal impact on the image resolution achieved. The passive cavitation image amplitude scales linearly with the cavitation emission energy. Cavitation images for both stable and inertial cavitation can be obtained from the same received data set.

Related References:
Haworth K. J. et al. 2012, Journal of the Acoustical Society of America, 132:544-553

PCI overlaid (hot colormap) on a B-mode (grayscale)
Echogenic liposomes were flowing (left to right) through a vessel phantom. Cavitation of the echogenic liposomes is induced with a clinical scanner in spectral Doppler mode (MI = 0.8). Loss of echogenicity in the B-mode images occurs at the same spatial location as subharmonic emissions in the passive cavitation images.