Ultrasound Cavitation/Microbubble Detection and Medical Applications

Over the past decades, different techniques have been investigated for detecting microbubbles. The purpose of this work is to review the state-of-the-art of medical microbubble detection along with therapeutic, monitoring, and diagnostic applications. The presence of microbubbles in the human body can be induced either through cavitation or exogenous introduction of bubbles. One of the effects of ultrasound is cavitation, or microbubble formation and collapse. Cavitation produces high pressures and temperatures, and microbubble expansion and then collapse close to cells can lead to cellular damage or hemorrhage in biological tissues. Cavitation is, in most cases, an undesired event in clinical diagnostic imaging. Considering that cavitation microbubble formation is largely unpredictable, ultrasound imaging may present a rare or yet unknown risk, particularly to fetuses and embryos. Although most therapeutic ultrasound modalities work based on physical and thermal effects of cavitation, the safety of treatment strongly depends on accurate knowledge of the location of the cavitation inception point. Cavitation detection is an important factor with respect to improving the safety of ultrasound imaging and therapy. It is essential to recognize the existence and location of cavitation inception points. In addition, the use of encapsulated microbubbles as contrast agents for diagnostic imaging, as vehicles for local drug or gene delivery, and as tools for microbubble and ultrasound therapy in thrombolysis has increased the demand for an accurate deep tissue microbubble detection technique. There have been many attempts to detect cavitation bubbles, but each contains its own limitations. There is no doubt that continuous discoveries and developments in microbubble detection modalities will lead to safer and more efficient therapeutic and diagnostic equipment.