In a research paper published Thursday (March 28) in the Institute of Physics publication Journal of Micromechanics and Microengineering, Dr. Rob Keynton and colleagues at the University of Louisville, Kentucky, and Michigan Technological University describe how they have designed and made an integrated miniature acoustical lens-transducer system that will focus ultrasound (high-frequency sound) very precisely, enabling medical researchers to look at very fine detail.

Very accurate imaging systems that use high-frequency ultrasound generated by a transducer are widely used in medical diagnostics and a variety of non-destructive testing applications (such as examining how a crack is spreading inside a material). Focusing the ultrasound beam means that a smaller region is examined by more intense sound waves, so that much more detailed information -- and a sharper image -- can be obtained.

A number of research groups have developed acoustical lenses to focus sound waves; the significant advance made by Dr. Keynton and his colleagues is that they have managed to create extremely small lenses attached directly to the transducer generating the sound.

An individual transducer crystal (made from PZT, lead-zirconate-titanate) with an attached wire was placed in a holding well -- in effect, a recessed hole -- and a liquid plastic (epoxy or Plexiglassâ) poured into the well.

Sophisticated and highly accurate micromachining techniques were then used to produce the concave structure needed to focus the ultrasound. The combined lens and transducer device is just 260 micrometers thick, with the lens itself being 160 micrometers thick with a diameter of 930 micrometers. For comparison, a human hair is around 100 micrometers wide.

The device is already being used in medical research by Dr. Keynton's group to look at the shear stress (dragging force) of blood on the artery walls and to see how this is connected to the development of cardiovascular diseases or conditions such as intimal hyperplasia -- when grafts block up again after a vascular bypass procedure.

Another likely medical application is in dermatology, where high-frequency ultrasound could be used to investigate skin cancers, telling the surgeon how deep a tumor is and where its edges are before surgery takes place.

The researchers would like to thank the National Science Foundation, Department of Defense, The Whitaker Foundation and Indus Instruments Inc for their past and current support of this research.

(Reference: The research paper "Design and fabrication of a miniaturizerd integrated, high frequency acoustical lens-transducer system" by Jinghong Li, Craig R Friedrich and Robert S Keynton is being published in the Journal of Micromechanics and Microengineering, Volume 12, Number 3, May 2002.)


[Contact: Dr. Rob Keynton]

01-Apr-2002