Ultrasound transducers and beams for combined imaging and therapy

Ultrasound technology for medical applications is rapidly evolving. This applies to both traditional applications such as imaging and diagnostics, but also new enabling possibilities in therapy, by stimulating the transport and absorption of drugs. An important element in this development are the production of two-frequency transducers that are also capable of delivering high power. This allows for much better discrimination between different tissue types (based on non-linear material properties) as well as combined imaging and stimulated medication. In this project, we have worked on developing and characterizing critical material technology for the production of such ultrasonic transducers. We have developed numerical models for designing optimal transducers, as well as the necessary software to be able to utilize the new information to create improved imaging. A small number of transducers have been produced and characterized, and initial clinical trials have been successfully performed.

Prosjektet har hatt høy betydning ved å resultere i nye ultralydprober og programvare som vil bli brukt videre til kliniske studier av forbedret kreftterapi med ultralydstimulert transport av medikamenter. Prosjektet har også bidratt til å etablere nye forretningsområder for de involverte bedriftene.

Ultrasound has been used for medical imaging for decades. Recent work has shown that ultrasound also can be used for mediation of drugs. However, this therapeutic use requires much higher transmited power, which today cannot be supplied by the imaging probes. The reason is that the wide bandwidth transducer requires matching layers with low density and stiffness to effectively couple the energy from the transducer to the human tissue. The piezoelectric element has a high acoustic impedance (high pressure with low displacement) whereas the human tissue has a low impedance (low pressure with high displacement). The main challenge has been to make acoustic matching layers that combine low density and stiffness, and at the same time provides sufficiently good thermal conductivity to allow efficient cooling. The use of new material technology based on metallised polymer spheres makes it possible to produce such matching layers. The aim of the Sleipnir project is to utilize these materials to design, manufacture and characterize a new generation dual frequency ultrasound transducers that can be used for combined drug delivery and state of the art imaging. The design and production of ultrasound transducers is a complex task, involving advanced material technology, manufacturing technology and advanced numerical modelling. An important activity is to understand the acoustic properties and response of the medium in which the transducer is designed to operate, to deduce the correct design parameters for the transducer element. This latter task is the focus of a large ongoing research project, headed by Professor Catharina Davies, Department of Physics, NTNU in collaboration by several researchers at the Cancer Clinic, StOlavs Hospital. The Sleipnir project will be working in a very close collaboration with this project, also sharing scientific staff.