Near-infrared light could allow researchers to see activity within the infant brain even while the tot wriggles and giggles.

Carrying out a brain scan on an active infant is next to impossible because standard techniques, such as functional magnetic resonance imaging (fMRI) and computed tomography (CT), rely on absolute stillness from the person being scanned, something that is unlikely to be achieved for hearing infacnts given how noisy the scanners can be.

"There have been some studies that obtained brain scans of infants while they were napping or sedated, but what we'd really like to do is to scan their brains when they're sitting on a parent's lap, seeing new things, hearing new words and interacting with the environment," explains Joseph Culver of the Washington University School of Medicine in St. Louis.

Culver and his colleagues have now developed an approach based on near infrared, known as high-density diffuse optical tomography (DOT), that does not require infant immobility. DOT will aid in basic research and could also help clinicians treat infant brain injury more effectively by facilitating non-invasive real-time monitoring of brain function.

"The DOT scanner, in contrast, is about the size of a small refrigerator, and it doesn't make any noise," Culver says. Diffuse optical brain imaging was originally developed in the 1990s by research groups in the United States, Europe and Japan.
To scan a patient or volunteer with high-density DOT, scientists attach a flexible cap that covers the exterior of the head above the brain region of interest. Inside the cap are fibre optic cables, some of which shine light on the surface of the head, and some of which detect that light as it diffuses through tissue. Moreover, near-infrared light passes through bone with relatively little attenuation, so researchers can use the diffusing light to determine blood flow and oxygenation in the brain's blood vessels, which acts as a proxy for activity in the brain itself.

Culver and his colleagues coupled the technique with tomography using the greater density of fibre optic cables available in a new scanning unit. To prove that this achieves sufficient resolution for functional brain imaging, they tested the technology on volunteers using retinotopic mapping, a standard functional brain imaging task based on vision. "Before the development of our high-density DOT system, detailed retinotopic maps like this weren't possible with non-invasive optical imaging."

In addition to enabling infant brain scans, high-density DOT should make it possible for neuroscientists to scan adults engaging in complex tasks that are difficult in the tight confines of an fMRI scanner, such as playing a game or engaging in conversation.

Related links:

• Proc Natl Acad Sci, 2007, 104, 12169-12174
• Optical Radiological Laboratory

Article by David Bradley