A team has combined micro-computed tomography (micro-CT) with Monte Carlo simulations and experimental measurements to characterise the light dose that actually reaches the brain in transcranial photobiomodulation devices. The work addresses a common gap in the field: the lack of rigorous quantification of how much near-infrared energy is truly deposited in deep tissue, beyond the nominal power rating of the device.

Transcranial photobiomodulation uses red or near-infrared light in the hope of modulating neuronal activity and treating neurological conditions, but scattering and absorption in skin, skull and meninges mean that only a small and highly variable fraction of photons reaches the cortex. Without reliable dosimetry, clinical studies are difficult to compare and reproduce.

The methodology starts from micro-CT images that reconstruct bone and tissue structure in enough detail to feed a Monte Carlo-type photon transport model. The simulations estimate the absorbed dose distribution as a function of depth and position, and the results are checked against experimental dosimetry to validate the model.

Combining individual anatomical imaging, stochastic light transport simulation and direct measurement offers a framework for tuning the dose delivered by each device and patient. In the long run, this kind of dosimetry could become a requirement to standardise photobiomodulation protocols and to interpret the results of ongoing clinical trials with confidence.