An Indispensable tool for ultrasound based diagnostics and therapies - Microbubbles

Microbubbles (MBs) are micrometre sized gas spheres comprising a biocompatible shell that provide vascular contrast for diagnostic ultrasound (US) imaging. MBs volumetrically oscillate in an ultrasonic field and scatter acoustic energy over a range of frequencies that can be separated from the tissue response. MBs can also provide organ perfusion rates by imaging their “wash-in” to a region of interest which can be correlated to vascular flow. When driven at higher acoustic pressures, localized biological effects can be induced, including increased tissue permeabilization, thermal effects and localised release of drugs that can be encapsulated in the MBs themselves. Both hydrophobic and hydrophilic drugs can be loaded on to MBs e.g. through the use of liposomal carriers or direct attachment of drug molecules to the bubble shell. Since the early 2000s, MB-based technologies have been well researched, though there was significant regulatory push back starting in 2006 based on a controversial clinical trial. From that point, both physicians and researchers have consistently demonstrated the robust safety of MBs as ultrasound contrast agents and their significant clinical utility. Within the last 5 years, more indications have been approved. A recent first-in-man clinical trial of therapeutic US with MBs reversibly opening the blood brain barrier has also been shown to be safe in amyotrophic lateral sclerosis patients. The following article outlines the coupling of US and MBs as a diagnostic and therapeutic platform with a particular focus on their application to the therapy of surgical diseases.