Micro lenses bring new focus to heart disease

A tiny ultrasound measurement system with a lens less than 1mm thick could help doctors treat cardiovascular disease.

A tiny ultrasound measurement system with a lens less than 1mm thick could help doctors treat cardiovascular disease.

The newly developed micro-acoustical lens-transducer system works by focusing ultrasound waves to allow researchers to view bodily phenomena in fine detail.

Developed by Dr Rob Keynton and colleagues at the University of Louisville, Kentucky, together with Michigan Technological University, the unit measures ‘shear stress’ – the force exerted on the wall of an artery by blood rushing past it.

During surgery three transponder and lens units are placed in the artery wall, each producing ultrasound signals. These are then bounced back to the unit, which records their rate of return and transmits this data to a computer, which calculates the rate of blood flow.

‘The unit works using the Doppler principle, just like a police radar gun,’ said Dr Keynton, head of the development team. ‘We are currently using it in animal trials, but we anticipate moving on to human applications in the future.’Acoustical lenses capable of focusing sound waves have been under R&D for some time, but the miniature size of the lenses connected to the sound-generating transducer is unique.

Although accurate transducer imaging systems are already used for applications such as investigating the spread of a crack inside materials, the focused ultrasound beam means that a smaller region is examined by intense sound waves, providing medics with a sharper image.

To create the system, an individual transducer crystal made from PZT (lead-zirconate-titanate) with an attached wire was placed in a Teflon-coated holding well. Liquid plastic was then poured in, and the units transferred to an oven to be cured, before the plastic was shaped into a precise concave lens using micromilling techniques with a laser-controlled positioning system.

The combined thickness is just 260 micrometres, while the lens has a diameter of 930 micrometres, and is 160 micrometres thick.

The instrument is already being used to investigate if shear stress affects the development of cardiovascular disease, as well as intimal hyperplasia, when artery grafts become blocked following a bypass operation. Another possible use is the measurement of skin cancers by dermatologists.