Based on new research at Washington University School of Medicine in St. Louis, researchers have further enhanced a brain scanning technology that follows what the brain is doing by illuminating dozens of microscopic LED lights on the head. This new age of neuroimaging is a wide improvement from previous methods and approaches; and avoids all radiation exposure and hulking magnets other scanners require.
The new optical approach to brain scanning is ideally suited for children and for patients with electronic implants, such as pacemakers, cochlear implants and deep brain stimulators (used to treat Parkinson's disease). The magnetic fields in magnetic resonance imaging (MRI) often disrupt either the function or safety of implanted electrical devices, whereas there is no interference with the optical technique.
The novel technology is called diffuse optical tomography (DOT). While researchers have been developing it for more than a decade, the method itself had been restricted to small regions of the brain. The new DOT device covers two-thirds of the head and for the first time can image brain processes taking place in several regions and brain networks such as those involved in language processing and daydreaming.
The results have since been published online in Nature Photonics.
"When the neuronal activity of a region in the brain increases, highly oxygenated blood flows to the parts of the brain doing more work, and we can detect that. It's roughly akin to spotting the rush of blood to someone's cheeks when they blush," said senior author and associate professor of radiology, Joseph Culver, PhD.
The scanner functions by identifying light transmitted through the head and recording the active changes in color of the brain tissue.
Even though DOT technology is now utilized in research settings, it has the potential to be useful in multiple medical situations as a substitute for functional MRI, which is the most commonly used imaging method for mapping human brain function. Functional MRI also tracks activity in the brain by changes in blood flow. And apart from greatly contributing to our current understanding of the human brain, fMRI is also employed to diagnose and observe brain disease and therapy.
Another commonly used imaging technology for mapping brain function is positron emission tomography (PET), which involves radiation exposure. Because DOT technology does not expose patients to radiation, several scans performed over time could be used to surveillence the progress of patients treated for brain injuries, developmental disorders such as autism, neurodegenerative disorders such as Parkinson's, and other diseases.
Unlike fMRI and PET, DOT technology is intended to be a portable device, so it could be utilized at a patient's beside or in the operating room.
"With the new improvements in image quality, DOT is moving significantly closer to the resolution and positional accuracy of fMRI. That means DOT can be used as a stronger surrogate in situations where fMRI cannot be used," said first author and postdoctoral research fellow, Adam T. Eggebrecht, PhD.
The researchers have numerous ideas for implementing DOT, including learning more about how deep brain stimulation helps Parkinson's patients, imaging the brain during social interactions, and studying what happens to the brain during general anesthesia and when the heart is temporarily stopped during cardiac surgery.
As for the current study, the researchers verified the performance of DOT by weighing its outcomes to fMRI scans. Data was gathered using the same subjects, and the DOT and fMRI images were aligned. They looked for Broca's area, a prime area of the frontal lobe used for language and speech production. The overlap between the brain region identified as Broca's area by DOT data and by fMRI scans was around 75 percent.
In a second bout of tests, researchers applied DOT and fMRI to spot brain networks that are active when subjects are in rest or daydreaming. Researchers' interests in these networks have risen exponentioally over the past decade as the networks have been linked to various different aspects of brain health and sickness, such as schizophrenia, autism and Alzheimer's disease. In these studies, the DOT data also demonstrated remarkable similarity to fMRI, picking out the same cluster of three regions in both hemispheres.
"With the improved image quality of the new DOT system, we are getting much closer to the accuracy of fMRI. We've achieved a level of detail that, going forward, could make optical neuroimaging much more useful in research and the clinic," said Culver.
While DOT doesn't let researchers look extensively deep into the brain, they can retrieve reliable data to a depth of about one centimeter of tissue. That centimeter holds some of the brain's most important and interesting areas with several higher brain functions, such as memory, language, and self-awareness represented.
During DOT scans, the subject wears a cap consisting of numerous light sources and sensors hooked to cables. The full-scale DOT unit takes up an area slightly larger than an old-fashioned phone booth, but Culver and his colleagues have constructed versions of the scanner so that they are positioned on wheeled carts. They continue to work to make the technology more portable.