Unusually detailed ultrasound images are providing ophthalmic doctors
in Canada with a means to diagnose and track eye diseases with greater precision
than before – but at no extra cost. The images come from the world’s first
ultrasound device for microscopic imaging of the eye.
Stuart Foster, an associate professor in the Department of Medical Biophysics
at the University of Toronto’s Sunnybrook Health Science Center, says that
ultrasound biomicroscopy allows physicians to examine eye tissue harmlessly
and in detail.
UBM has already been used on around 100 patients. The device allows
doctors to modify their scheme of treatment by monitoring the development
of lesions and tumours, says Charles Pavlin, the co developer of the system.
It resolves images more finely than normal ultrasound, and can even manage
features between 40 and 50 millionths of a metre across. UBM focuses on
areas 4 millimetres square compared with 4 centimetres square for normal
Because resolution rises in tandem with the frequency of the sound waves
used in ultrasound devices, UBM works in a range between 50 to 100 megahertz,
compared with between 3 and 10 megahertz for conventional devices.
To achieve the desired resolutions, Foster and colleagues had to devise
new transducers for the device. These are 1-millimetre rods coated with
thin films of materials – usually zinc oxide – which focus sound and act
as ‘acoustic lenses’. They resolve better with higher frequencies. The team
at Toronto cracked the problem by coating the transducers with different
materials, either poly(vinylidene fluoride) or lead zirconate titanate.
The penalty for the higher resolution is that the devices can only image
shallow layers of tissue. As resolution increases, penetration of sound
waves into tissue decreases. UBM works to depths of about 4 millimetres,
which is ideal for many ophthalmic applications, but Foster expects improved
electronics and transducers to extend the depth of penetration and the breadth
He speculates that UBM might eventually lead to the development of tiny
ultrasound scanning devices to insert into the body on catheters and needle-tip
probes. These, he says, could be used for diagnostic applications inside
blood vessels, bile ducts and the gastric canal.