Passive cavitation imaging with ultrasound arrays

Abstract

A method is presented for passive imaging of cavitational acoustic emissions using an ultrasound array, with potential application in real-time monitoring of ultrasound ablation. To create such images, microbubble emissions were passively sensed by an imaging array and dynamically focused at multiple depths. In this paper, an analytic expression for a passive image is obtained by solving the Rayleigh-Sommerfield integral, under the Fresnel approximation, and passive images were simulated. A 192-element array was used to create passive images, in real time, from 520-kHz ultrasound scattered by a 1-mm steel wire. Azimuthal positions of this target were accurately estimated from the passive images. Next, stable and inertial cavitation was passively imaged in saline solution sonicated at 520 kHz. Bubble clusters formed in the saline samples were consistently located on both passive images and B-scans. Passive images were also created using broadband emissions from bovine liver sonicated at 2.2 MHz. Agreement was found between the images and source beam shape, indicating an ability to map therapeutic ultrasound beams in situ. The relation between these broadband emissions, sonication amplitude, and exposure conditions are discussed.

Experimental demonstration of passive acoustic imaging in the human skull cavity using CT‐based aberration corrections

“…However, the information obtained from a single-element PCD is fundamentally limited due to the inherent trade-off between the volume of sensitivity and spatial specificity of the device. The use of multielement arrays, combined with passive beamforming algorithms borrowed from other fields, [45][46][47][48] has been shown to overcome this limitation and enable spatial mapping of cavitation activity during the application of FUS in both in vitro [49][50][51][52][53][54][55][56][57][58][59][60][61][62] and in vivo [63][64][65][66][67] settings. The integration of passive imaging during mechanicalbased FUS brain therapies would make the procedures practical, by providing a method for real-time treatment monitoring and control.…”

Passive imaging with pulsed ultrasound insonations

“…28,29 More recently, PCDs using multiple-element arrays have been shown to reduce the limitations of focused and unfocused PCDs by allowing for spatial resolution over a large area. Farny et al 23 and Salgaonkar et al 30 used modified diagnostic scanners with the ultrasound array transmit turned off and the array in a passive detection state. The cavitation was induced by a separate therapy transducer.…”

Spatial specificity and sensitivity of passive cavitation imaging for monitoring high-intensity focused ultrasound thermal ablation in ex vivo bovine liver

“…Lesions were formed by a 30 s HIFU exposure at 1.1 MHz. Cavitation emissions were recorded with an imaging array and beamformed using established procedures (Salgaonkar et al, 2009). Comparison of the lesion location, as assessed optically, and the location of cavitation emissions, as assessed from PCIs, was performed using ROC curves.…”

“…Focused single-element PCDs provide good spatial specificity, whereas unfocused single-element PCDs have a larger region over which they are sensitive. To overcome this limitation, several recent investigators have developed and implemented passive cavitation imaging (Gyöngy et al, 2008;Farny et al, 2009;Salgaonkar et al, 2009;Haworth et al, 2012;Jensen et al, 2012).…”