Optical technique finds the pain in the brain

Scientists at the University of Illinois have created a non-invasive diagnostic tool that can study changes occurring at the surface of the brain.

Scientists at the University of Illinois have developed a non-invasive diagnostic tool that can study changes occurring at the surface of the brain because of brain activity.

The technique is based upon near-infrared spectroscopy and is said to be simpler to use and less expensive than other methods such as functional magnetic resonance imaging and positron emission tomography.

‘Whenever a region of the brain is activated – directing movement in a finger, for example – that part of the brain uses more oxygen,’ said Enrico Gratton, a UI professor of physics. ‘Our technique works by measuring the blood flow and oxygen consumption in the brain.’

The optical technique is fast and simple to use, Gratton said.

First, light emitted by near-infrared laser diodes is carried through optical fibres to a person’s head. The light penetrates the skull where it assesses the brain’s oxygen level and blood volume.

The scattered light is then collected by optical fibres, sent to detectors and analysed by a computer.

By examining how much of the light is scattered and how much is absorbed, Gratton and his colleagues in the university’s Laboratory for Fluorescence Dynamics can map portions of the brain and extract information about brain activity.

‘By measuring the scattering, we can also determine where the neurons are firing,’ Gratton said. ‘This means we can simultaneously detect both blood profusion and neural activity.’

The technique could be used in many diagnostic, prognostic and clinical applications.

‘For example, it could be used to find hematomas in children, or to study blood flow in the brain during sleep apnea,’ Gratton said. ‘It could also be used to monitor recovering stroke patients on a daily, or even hourly, basis — something that would be impractical to do with MRI.’

To validate the technique, Gratton and Vladislav Toronov, a postdoctoral research associate at the university’s Beckman Institute for Advanced Science and Technology, compared haemoglobin oxygen concentrations in the brain obtained simultaneously by near-infrared spectroscopy and by functional MRI — the current ‘gold standard’ in brain studies.

‘Both methods were used to generate functional maps of the brain’s motor cortex during a periodic sequence of stimulation by finger motion and rest,’ Gratton said. ‘We demonstrated spatial congruence between the haemoglobin signal and the MRI signal in the motor cortex related to finger movement.’

The researchers also demonstrated collocation between haemoglobin oxygen levels and changes in scattering due to brain activities. ‘By having a volunteer move different fingers, we could see an increase in perfusion in different areas of the brain,’ Gratton said. ‘The changes in scattering associated with fast neuron signals came from exactly the same locations.’