Microbubble cavitation imaging

Abstract

Ultrasound cavitation of microbubble contrast agents has a potential for therapeutic applications such as sonothrombolysis (STL) in acute ischemic stroke. For safety, efficacy, and reproducibility of treatment, it is critical to evaluate the cavitation state (moderate oscillations, stable cavitation, and inertial cavitation) and activity level in and around a treatment area. Acoustic passive cavitation detectors (PCDs) have been used to this end but do not provide spatial information. This paper presents a prototype of a 2-D cavitation imager capable of producing images of the dominant cavitation state and activity level in a region of interest. Similar to PCDs, the cavitation imaging described here is based on the spectral analysis of the acoustic signal radiated by the cavitating microbubbles: ultraharmonics of the excitation frequency indicate stable cavitation, whereas elevated noise bands indicate inertial cavitation; the absence of both indicates moderate oscillations. The prototype system is a modified commercially available ultrasound scanner with a sector imaging probe. The lateral resolution of the system is 1.5 mm at a focal depth of 3 cm, and the axial resolution is 3 cm for a therapy pulse length of 20 µs. The maximum frame rate of the prototype is 2 Hz. The system has been used for assessing and mapping the relative importance of the different cavitation states of a microbubble contrast agent. In vitro (tissue-mimicking flow phantom) and in vivo (heart, liver, and brain of two swine) results for cavitation states and their changes as a function of acoustic amplitude are presented.

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.…”

Influence of nesting shell size on brightness longevity and resistance to ultrasound-induced dissolution during enhanced B-mode contrast imaging

“…Microbubbles also increase the absorption of sonic energy through a mechanism known as cavitation [6]. An ultrasonic wave causes the microbubbles to oscillate with a wall velocity on the order of tens to hundreds of meters per second [5].…”

“…An ultrasonic wave causes the microbubbles to oscillate with a wall velocity on the order of tens to hundreds of meters per second [5]. As ultrasound interacts with microbubbles through expansion and contraction during negative and positive pressure phases, the microbubbles undergo sustained oscillations, a process known as stable cavitation [6]. As you increase the peak negative pressure, the microbubble will expand so large, typically accepted as twice its resting radius [7], that upon subsequent contraction it implodes.…”

Diagnostic imaging of molecular-targeted nanorods simultaneously exposed to light and sound

“…For short duration, low amplitude excitation inertial cavitation could be generated near cells, but not result in any significant damage [18]. This study aimed to demonstrate that this could be achieved using a custom ultrasound imaging system at exposure limits that are safe for diagnostic imaging.…”