16 Apr 2008
An optical technique for diagnosing Alzheimer's disease in living patients has been proposed by researchers in the US.
“Near infrared light can be used to probe the brain while the patient is still alive.”
Alzheimer sufferers could benefit from an optical spectroscopy method that uses near infrared light to probe brain tissue. The method involves detecting light that is scattered by the tissue, offering a non-invasive way of detecting the disease early (Optics Letters 33 624).
"Currently, there is no definitive test to diagnose Alzheimer's disease during life," Eugene Hanlon, a researcher from the US Department of Veterans Affairs, told optics.org. "Near infrared light can propagate through centimeters of tissue, to probe the brain and other deep structures, non-invasively while the patient is still alive. This means that holes do not need to be drilled and exogenous markers do not need to be used."
Additional strengths of the technique include relatively low cost (hence wide accessibility), molecular (chemical) and cellular (structural) level diagnostic information and obviation of exogenous labels.
In the experiment, brain tissue samples were taken from Alzheimer's patients during an autopsy and compared with normal control brain tissue. The tissue was probed with near infrared light and the resulting transmission and reflectance spectra were analyzed over the wavelength range 470-1000 nm.
"Incident light from a water-filtered xenon arc source is coupled into the central fibre optic of a fibre bundle and delivered to 1 mm thick tissue slabs," explained Hanlon. "Six detection fibres with core diameters of 200 µm and an NA of 0.22 are arranged concentrically around the delivery fibre to collect the reflected light. This light is then dispersed by an imaging spectrograph onto a CCD detector."
The group found that reflectance spectroscopy in the range 670-970 nm was significantly different for tissue samples with the disease compared with the normal control tissue. "We found that neuritic plaques, which accumulate in the brain of Alzheimer sufferers, increases light scattering compared with normal brain tissue," commented Hanlon.
The results are a positive step towards diagnosing Alzheimer's disease and the team is now developing and testing clinical applications of these methods.