Scientists have developed a new technique for non-invasive brain imaging – and it involves shining light all the way through the head, from one side to the other.

Currently the best portable, low-cost method for monitoring the brain is functional near-infrared spectroscopy (fNIRS). Unfortunately, this can only penetrate a few centimeters down, meaning bigger, bulkier MRI machines are needed to probe deeper layers of the brain.

A new method, developed by a team from the University of Glasgow in Scotland, expands the sensitivity of fNIRS to shine light all the way through the complex combinations of bone, neurons, and tissue that make up our heads.

Doing so required a few tweaks: the researchers increased the strength of the near-infrared laser (within safe boundaries, of course), while also putting in place a more comprehensive collection setup.

Even with these adjustments, only a small trickle of photons made it from one side of the head to the other during experiments. However, it’s a promising start for portable imaging methods that go deeper, giving us crucial insight into what’s happening inside our skulls without opening them up.

“These findings uncover the potential to extend non-invasive light based on brain imaging technologies to the tomography of critical biomarkers deep in the adult human head,” write the researchers in their published paper.

There are quite a number of caveats to mention here. The process was only successful with one out of eight study participants: a man with fair skin and no hair on his head. It needs a very specific setup, and an extended scanning time – around 30 minutes.

Those limitations are all acknowledged by the researchers, but they sacrificed certain variables (such as speed) to try and prove that it was possible to get light all the way through a human head via fNIRS – and they succeeded.

Computer models based on detailed 3D head scans were used to predict the movement of photons through the skull. These matched up closely with the actual light collected, adding further credibility to the results.

What’s more, the research also found that light didn’t scatter at random through the head, but rather followed preferred paths – including through parts that were more transparent, like those filled with cerebrospinal fluid. That knowledge could help brain scans be better targeted in the future.

“Different source positions on the head can then selectively isolate and probe deep regions of the brain,” write the researchers.

The advantages of fNIRS are that it’s a relatively inexpensive and compact technology. Imagine scans for strokes, brain injuries, and tumors that are more accessible for a wider range of people.

As future imaging devices are developed, this research should prove useful for techniques that go deeper into the brain – even if it might be a while before we can get light through the entire head in a timeframe that’s practically useful.

We know that brain scans have tremendous value in everything from understanding adolescence in youngsters to treating disease towards the end of our lives, so there’s a huge amount of potential here.

“Optical modalities for noninvasive imaging of the human brain hold promise to fill the technology gap between cheap and portable devices such as electroencephalography (EEG) and expensive high-resolution instruments such as functional magnetic resonance imaging (fMRI),” write the researchers.

The research has been published in Neurophotonics.