Scientists from Washington University School of Medicine in St. Louis have progressed the field of neuroimaging by developing a new generation of optical brain scanning technology that supersedes previous optical methods. The imaging system, which involves illuminating the head with numerous light-emitting diodes (LEDs), was able to image brain function in a detailed manner across numerous areas of the brain during both language tasks and daydreaming. The study has been published in Nature Photonics.
Mapping brain activity via neuroimaging techniques has dramatically enhanced our comprehension of brain function. There are two main techniques used to image the brain; positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). While these techniques give highly detailed brain maps, they are limited in their usage in some circumstances. This is because PET uses ionizing radiation and therefore cannot be used as an experimental procedure in children. fMRI can interfere with implanted electronic devices such as pacemakers or deep brain stimulators used in Parkinson’s patients.
Scientists have been working on this new technique, called diffuse optical tomography (DOT), for over a decade but previous systems were limited to imaging individual brain regions as opposed to multiple functional systems at the same time. By increasing the area of the head covered by the instrument, this new system can image the processes occurring in multiple different networks simultaneously.
In order to create brain images, participants are given a cap studded with LED lights which illuminate the head. Dynamic changes in the brain tissue that occur when certain regions become activated can then be detected. “When the neuronal activity of a region of the brain increases, highly oxygenated blood flows to the parts of the brain doing more work, and we can detect that,” said senior author and associate professor of radiology Joseph Culver in a news-release. “It’s roughly akin to spotting the rush of blood to someone’s cheeks when they blush.”
While DOT is not capable of imaging deep brain structures, the maps generated from a tissue depth of only around a centimeter can provide useful information on numerous regions involved in higher brain functions such as memory.
One advantage DOT has over PET and fMRI is that the device is portable and can therefore be used in a wider variety of settings. The device is currently around the size of a phone box, although they are currently attempting to make it easier to transport. According to first author of the study Adam Eggebrecht, images generated by DOT technology are moving toward fMRI quality; therefore this could be used as a surrogate in situations where fMRI can’t be used.
In order to investigate the performance of DOT, researchers in this study took brain images of the same individuals using both DOT and fMRI for comparison. When they aligned the images and searched for a particular region known as Broca’s area, which is involved in language and speech, the overlap for the identified region was around 75%.
The team then used both of these techniques to image regions of the brain that are active during rest or daydreaming, called default mode networks. They found that both sets of images were remarkably similar.
“With the improved image quality of the new DOT system, we are getting much closer to the accuracy of fMRI,” said Culver. “We’ve achieved a level of detail that, going forward, could make optical neuroimaging much more useful in research and the clinic.”