Physicists have, for the first time, detected light that passed through an adult human skull, traveling 15.5 cm and undergoing significant signal attenuation. The study, published in Neurophotonics, used a pulsed laser and a time-correlated single-photon detection system, capturing about one photon per second after 30 minutes of data collection. This achievement opens prospects for non-invasive diagnostics of deep brain layers.
In the experiment, laser pulses were directed at one side of the head, while an ultra-sensitive detector on the opposite side captured surviving photons that passed through skin, skull, cerebrospinal fluid, and brain tissue. Computer models predicted the light’s trajectories, primarily through cerebrospinal fluid, which was experimentally confirmed. The technology enabled data collection from sulci, midbrain nuclei, and the cerebellum—regions inaccessible to methods like fNIRS, which penetrate only 4 cm.
The clinical significance of the study lies in its potential for diagnosing subcortical hemorrhages and tumors in settings where MRI is unavailable. However, success was achieved only with one subject with light skin and no hair, indicating the influence of biological factors. The long data collection time and the use of 1.2-watt lasers, close to safety limits, require refinement for practical application.
This work lays the foundation for portable optical systems combining the deep resolution of fMRI with the convenience of EEG. With advancements in detection technologies and computational methods, non-invasive brain imaging could become more accessible, revolutionizing the diagnosis of neurological disorders.
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