Optical technique studies brain activity without surgery on skull

Aug. 8, 2001
The technique based upon near-IR spectroscopy is reportedly simpler to use and less expensive than other methods such as functional magnetic resonance imaging and positron emission tomography.

A non-invasive diagnostic tool that can study changes occurring at the surface of the brain because of brain activity has been developed by scientists at the University of Illinois (Champaign, IL). The technique is based upon near-infrared (IR) spectroscopy and is 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 fibers 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 fibers, sent to detectors and analyzed 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 researcher at the university�s Beckman Institute for Advanced Science and Technology, compared hemoglobin 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 hemoglobin signal and the MRI signal in the motor cortex related to finger movement."

The researchers also demonstrated collocation between hemoglobin 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."

The National Institutes of Health supported the research.

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