Ultrasound-triggered drug release from vibrating microbubbles

Abstract

Diagnostic medical ultrasound may have a slightly longer history than what you expected. Its root dates back to 1930s and 1940s, when Theodore Dussik, a psychiatrist and neurologist, and his brother Friederich used a 1.5 MHz source to record signal variations after transmitting the wave through the human brain. Although these images were later shown to measure the skull bone attenuation instead of brain ventricles as the Dussik brothers had believed, it was one of the earliest attempts to scan an in vivo organ (White 1988). The real developments of medical ultrasound imaging initiated after Second World War, since 1950s, when the “pulse echo” technique was adapted from military sonar and radar. For the practicality to position the setup for medical imaging, only a single transducer was used to measure the reflected wave from the target sample in contrast to transmission, which measures the wave transmitted through the medium by a sending transducer and a separate receiving transducer. In early 1950s, John Wild and John Reid developed the first hand-held imaging device which was applied to image breast cancer tumors (Newman and Rozycki 1998). However, it was not until 1960s and 1970s, with the development of electronics, these pioneering works truly came to fruition. The static B-mode imaging was replaced by real-time imaging modalities thanks to new techniques such as phased linear arrays (Seibert 1995). One of the major breakthroughs (which is also of special meaning to the author) is the multi-element linear arrays developed by the group headed by Professor Nicolaas Bom at Thoraxcenter, Erasmus medical center Rotterdam. The probe face consists of 20 crystals which can produce 20 scan lines in total. Figure 1.1 shows the design of the probe and the real-time cardiac image it produced. This early simple concept has later evolved into the more complicate real-time scanners that are widely available today. The later combination of real-time imaging with pulsed wave Doppler technique enabled accurate measurements of the blood flow, which greatly benefited diagnostic echocardiography.