Discover how Diffuse Optical Tomography (DOT) transforms traditional fNIRS into 3D brain imaging—bringing richer spatial resolution and new research possibilities.
Diffuse Optical Tomography (DOT) is quietly revolutionizing how we approach non-invasive brain imaging. For years, researchers using functional Near-Infrared Spectroscopy (fNIRS) have been able to observe cortical activity through light-based measurements of hemodynamics. But traditional fNIRS has always faced a spatial limitation: the method collects signals from narrow, isolated channels, with each channel essentially viewing a thin column of tissue between an emitter and detector. While powerful in its simplicity and portability, this setup leaves a great deal of the “bigger picture” of brain activity unobserved.
DOT is changing that.
The Limitation of Single-Channel Views
To understand what DOT improves, it helps to first appreciate how conventional fNIRS works. A single source-detector pair tells us about hemodynamic changes occurring along a restricted path beneath the scalp—effectively capturing the activity of a small cortical volume located between those two points. Channels are spatially distinct and non-overlapping, which means that brain activity is sampled in discrete patches rather than as a continuous map.
This is similar to trying to understand a city’s traffic by only observing isolated intersections—you may get local information, but you won’t see how traffic flows across the entire network.
How DOT Breaks Through
Diffuse Optical Tomography addresses this limitation by creating high-density arrays of overlapping fNIRS channels. The first key change involves how the optodes—light sources and detectors—are arranged. DOT moves beyond the constraints of standard EEG-based placement systems (such as 10–10 or 10–5 layouts) because these cannot provide the small inter-optode distances required for effective DOT. Instead, DOT systems use custom-designed caps—such as ninjacaps—that support a range of source-detector distances, typically from about 15–17 mm up to 40 mm.
Why is this range of distances important? When multiple source-detector pairs overlap spatially at different depths and angles, it becomes possible to infer the underlying distribution of optical absorption within the tissue—in other words, to reconstruct a 3D image of where brain activity is occurring.
In technical terms, the process involves running photon migration models—advanced simulations (often based on Monte Carlo methods) that describe how light scatters and is absorbed as it moves through biological tissue. By comparing actual measurements from the dense array to the predictions of these models, researchers can solve what’s known as an inverse problem: estimating where in the brain the observed hemodynamic changes originated. The result is a volumetric, depth-resolved map of cortical activation.
If traditional fNIRS is like peeking through keyholes into the brain, DOT is like stepping into the room with a panoramic camera.
From Keyholes to Panoramic Views
If traditional fNIRS is like peeking through keyholes into the brain, DOT is like stepping into the room with a panoramic camera. The spatial resolution improves dramatically because multiple overlapping measurements allow the reconstruction algorithm to sharpen and localize the observed activity.
Moreover, by combining short-separation channels (which measure superficial scalp signals) with longer channels (which penetrate deeper), DOT can better isolate true cortical responses from confounding superficial artifacts. This capability is crucial for producing clean and accurate images of brain function.
Practical Gains and New Possibilities
What does this mean for neuroscience and clinical research? DOT enables scientists to observe brain activity with significantly greater spatial precision—approaching the resolution of functional MRI (fMRI) in some contexts, but in a much more portable and wearable form factor.
It allows researchers to go beyond detecting whether some activation occurred and instead begin mapping which specific cortical regions are involved in a given task. For example, studies using DOT have demonstrated its ability to resolve fine-grained retinotopic maps of the visual cortex or to track functional connectivity across different brain networks.
DOT also extends the reach of neuroimaging into environments where MRI is impractical or impossible: bedside monitoring of newborns and stroke patients, cognitive testing in VR environments, and studies of real-world interactions—all become viable with wearable DOT systems.
Looking ahead
DOT bridges the gap between the accessibility of fNIRS and the spatial insight of fMRI, delivering wearable 3D brain imaging. It promises richer neuroscientific insight, from lab experiments to clinical applications—and we’re excited to bring this to our community.
At Cortivision, we are closely following the exciting developments around DOT and actively exploring how this powerful method can complement and extend the capabilities of fNIRS. As the technology continues to mature, we look forward to seeing how the global research community will apply DOT to new scientific questions and real-world challenges.