Otago breakthrough in combined scanning approach

University of Otago physicist Dr Jevon Longdell examines a transparent silicate crystal containing atoms of the rare metal praseodymium which are excited by a laser beam and used to store light. Photo by Peter McIntosh.

University of Otago physicists have achieved a technical breakthrough which could eventually lead to improved body scanners, using a combination of ultrasound and lasers.

Such a combined scanning approach - called ''ultrasound-modulated optical tomography'' (UOT) - was first proposed as a method for early cancer detection in soft tissue in 1993 but persistently difficult technical problems have since severely limited its development.

Research leader Dr Jevon Longdell was previously part of an Australian-led team whose work featured prominently in the prestigious journal Nature in 2010, for developing the world's most efficient quantum memory for light.

The ANU-led scientists had pioneered a technique to stop and control light from a laser, manipulating electrons in a crystal cooled to about -270degC, about 3deg above absolute zero.

The Otago research team, which included Dr David McAuslan - now at the University of Queensland - and Dr Luke Taylor, recently used some of the earlier techniques, initially used in a bid to develop a highly-powerful quantum computer. And the researchers applied the methods, successfully, to the UOT challenges.

''It's exciting that we currently have world-beating performance and that this research might be applied in the near future,'' Dr Longdell said.

''The promise of such an imaging system is that it will one day give doctors more information about the characteristics of pieces of tissue, and, for example, better distinguish between dangerous and harmless growths.''

The Otago group had combined ''quantum memory techniques with the optical detection of ultrasound'', and achieved ''record sensitivity''.

Both light and ultrasound were used extensively for medical imaging, each with benefits and drawbacks.

Optical imaging techniques, using lasers, were ''very sensitive'', but the light scattered in biological tissue, limiting penetration depth.

Ultrasound imaging was less sensitive but could ''image deep into tissue without significant scattering''.

It was hoped to ''combine the best aspects of both''.

The researchers should be able to use their crystal-related filter to make ''high quality 3D images of tissues'' and further development work was under way. A scientific paper by the researchers at Otago's Jack Dodd Centre for Photonics and Ultra-Cold Atoms was published in the international journal Applied Physics Letters late last year, and recently highlighted by Nature Photonics.

Human tissues vibrated in the presence of ultrasound and there were very slight changes in the frequency of light waves when they encountered the vibrations.

Otago researchers had used ''more sophisticated filters'' to detect the changes.

- john.gibb@odt.co.nz