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Advance in Brain Imaging
Brain imaging is becoming an increasingly important tool in many
research areas, including sleep, addiction and other behaviors,
and in diseases such as autism, Alzheimer’s disease and Parkinson's
disease. Its expanding use is driving the development of new, more
flexible tools. Researchers have now developed a high-performance,
portable system that offers unique advantages over current brain
imaging systems.
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The large scanners currently in use make brain imaging difficult
in many situations—for example, with patients in intensive
care units, research subjects performing complex tasks, or for
infants and young children who need sedation. Diffuse optical imaging
(DOI) is a mobile system that uses a small, flexible imaging cap.
In contrast to positron emission tomography (PET), which uses ionizing
radiation, DOI uses safe, infrared light for imaging. DOI detects
blood dynamics in a manner similar to functional MRI (fMRI), which
primarily measures levels of one form of hemoglobin, the molecule
that carries oxygen in our blood. DOI can measure levels of hemoglobin
both when it is carrying oxygen and when it isn’t, enabling researchers
to form a more complete picture of blood activity in the brain.
Despite these advantages, however, DOI has been limited by its
low resolution, lack of ability to measure area volumes and the
complexity of the equipment.
A research team led by Dr. Joseph Culver of the Washington University
School of Medicine set out to develop a more advanced optical imaging
system with improved image quality. Their work was supported in
part by NIH’s National Institute of Neurological Disorders and
Stroke (NINDS) and National Institute of Biomedical Imaging and
Bioengineering (NIBIB). In the online edition of Proceedings
of the National Academy of Sciences on July 6, 2007, they
reported the development of a high-performance, high-density diffuse
optical tomography (DOT) system.
The researchers demonstrated their system by functionally mapping
the adult human visual cortex. This brain region is ideal for testing
new brain imaging techniques because its structure and function
have already been comprehensively mapped using other methods. The
results from the high-density DOT system were consistent with previous
fMRI and PET mappings of the visual cortex.
The study demonstrated that high-density DOT can be a practical
and powerful tool for functional brain mapping. The system is also
scalable, which will allow for mapping larger brain regions. The
researchers anticipate that this advance will open the path for
a wide range of new studies of both developing and diseased brains.
—by Harrison Wein, Ph.D.
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