Particle Technology for High-Performance Ultrasound Transducers for Medical Imaging and Therapy

The project develops new material technology based on metallized polymer particles for use in advanced acoustic matching layers for ultrasound technology designed for medical imaging and therapy. The main challenge is to adapt the high acoustic impedance of the piezo ceramic element to the low impedance of the body tissue and at the same time be able to efficiently remove the heat generated. With traditional technology these properties are difficult to obtain, as high thermal conductivity requires a high degree of filling of either metals or certain metal oxides, which gives much too dense and rigid matching layers. By using metallized polymer particles, we can combine the needed acoustic impedance with good thermal conductivity. We have now developed experimental methods to study the acoustic and thermal properties of the new matching layers. Simulation methods to study the acoustic and thermal properties of matching layers with different thicknesses and different particles have been developed. Manufacturing of test transducers where the different properties can be analysed in built transducer has been planned and will soon be initiated. A scientific paper which analyses matching layers in a two-frequency transducer has been published. Two scientific papers regarding the thermal and electrical conductive transport in materials developed for acoustic matching layers have also been published. A second scientific paper is finished and now ready for submission. This paper presents an analysis of a transducer design for improved lateral heat transport using the materials developed in this project. In the last phase of the project the work has been focused on building and testing of test transducers. Two different production methods have been studied for creating matching layers from the new material. Four test transducers are finished, two with and two without metallized polymer particles for comparison of heat conduction. Preliminary temperature measurements have been performed, and they are looking promising, resulting in lower temperatures in the transducers with metallized polymer particles than without. The project is now finished, but further testing and verification of the results will continue after the end of the project, and the results will be utilized in new projects.

Prosjektet har resultert i både ny kunnskap og ny kompetanse for bedriftene involvert i prosjektet. På sikt vil de lovende resultatene fra prosjektet kunne resultere i både nyskapende produkter samt forbedrede og billigere produksjonsmetoder som har anvendelser for et bredt spekter av næringslivet hvor ultralyd benyttes. Aktuelle applikasjoner inkluder blant annet medisinsk avbilding og terapi, sonar og undervannskommunikasjon.

The project addresses development of heat conducting acoustic matching layers for ultrasound transducers, utilizing mono disperse polymer spheres coated with thermally conducting layers mixed in a polymer resin. The matching layers will be used to improve cooling of high power, dual frequency transducers for combined medical imaging and cancer therapy. The technology also improves the manufacturing accuracy of thickness and acoustic impedance and reduces manufacturing cost of the matching layers. A new method of ultrasound imaging (SURF imaging) requires dual frequency transducers, e.g. 0.3 and 3 MHz or 1 and 10 MHz. For cancer therapy, ultrasound is used for i) heating of tissue, ii) improved transport of drugs to cancer cells using acoustic radiation force, and iii) stable cavitation of micro bubbles that opens cell membranes to allow transport of large molecular drugs and genes into the cancer cells. Heating and ultrasound radiation force require a high ultrasound frequency, e.g. 10 MHz, while cavitation prefers a low frequency, e.g. 1 MHz. Ultrasound radiation force is also used diagnostically in shear wave imaging that gives the elastic stiffness of tissues, improving imaging of cancer tumors that have different elasticity than surrounding tissue. The method also has potential to characterize other tissues, for example estimate amount of fat in muscle tissue. Both radiation force and tissue heating require high transmitted power, causing problems with over-heating of transducers with current transducer technology. The new technology hence opens for combined transducers for cancer diagnosis and high power therapy. In addition to improved imaging and therapy of cancer and atherosclerosis, the improved imaging and tissue characterization is useful in breeding of stem-fish and -animals, for example to determine fat content in the muscles that has importance for the taste of food products.