Seminar of Michiel Postema

The sonic tricorder: ultrasound, bubbles and therapy

Ultrasonic imaging is becoming the most popular medical imaging modality, owing to the low price per examination and its safety. However, blood is a poor scatterer of ultrasound waves at clinical diagnostic transmit frequencies. For perfusion imaging, markers have been designed to enhance the contrast in B-mode imaging. These so-called ultrasound contrast agents consist of microscopically small gas bubbles encapsulated in biodegradable shells. In this presentation, the physical principles of ultrasound contrast agent microbubble behaviour and their adjustment for drug delivery including sonoporation are described. It is a challenging task to quantify and predict which bubble phenomenon occurs under which acoustic condition, and how these phenomena may be utilised in ultrasound-assisted therapy. Aided by high-speed photography, our improved understanding of encapsulated microbubble behaviour may lead to more sophisticated detection and delivery techniques. Still many challenges appear, especially related to signal and image processing. More sophisticated methods use quantitative approaches to measure the amount and the time course of bolus or reperfusion curves, and have shown great promise in revealing effective tumour responses to anti-angiogenic drugs in humans before tumour shrinkage occurs. These are beginning to be accepted into clinical practice. In the long term, targeted icrobubbles for molecular imaging and eventually for directed anti-tumour therapy are expected to be tested.