Radford Jack, Gradauskas Vytautas, Mitchell Kevin J, Nerenberg Samuel, Starshynov Ilya, Faccio Daniele
University of Glasgow, School of Physics and Astronomy, Glasgow, United Kingdom.
Neurophotonics. 2025 Apr;12(2):025014. doi: 10.1117/1.NPh.12.2.025014. Epub 2025 May 28.
The highly scattering nature of near-infrared light in human tissue makes it challenging to collect photons using source-detector separations larger than several centimeters. The limits of detectability of light transmitted through the head remain unknown. Detecting photons in the extreme case through an entire adult head explores the limits of photon transport in the brain.
We explore the physical limits of photon transport in the head in the extreme case wherein the source and detector are diametrically opposite.
Simulations uncover possible migration pathways of photons from source to detector. We compare simulations with time-resolved photon counting experiments that measure pulsed light transmitted through the head.
We observe good agreement between the peak delay time and width of the time-correlated histograms in experiments and simulations. Analysis of the photon migration pathways indicates sensitivity to regions of the brain well beyond accepted limits. Source repositioning can isolate sensitivity to targeted regions of the brain, including under the cerebrum.
We overcome attenuation of and detect photons transmitted through an entire adult human head for a subject with fair skin and no hair. Photons measured in this regime explore regions of the brain currently inaccessible with noninvasive optical brain imaging.
近红外光在人体组织中的高散射特性使得使用源探测器间距大于几厘米来收集光子具有挑战性。透过头部传输的光的可探测极限仍然未知。在极端情况下通过整个成人头部检测光子可探索光子在大脑中传输的极限。
我们在源和探测器处于直径相对的极端情况下探索光子在头部传输的物理极限。
模拟揭示了光子从源到探测器的可能迁移路径。我们将模拟结果与时间分辨光子计数实验进行比较，该实验测量透过头部传输的脉冲光。
我们观察到实验和模拟中时间相关直方图的峰值延迟时间和宽度之间有良好的一致性。对光子迁移路径的分析表明对大脑区域的敏感度远超公认极限。源重新定位可以将敏感度隔离到大脑的目标区域，包括大脑下方。
对于皮肤白皙且无毛发的受试者，我们克服了衰减并检测到了透过整个成人头部传输的光子。在此状态下测量的光子探索了目前非侵入性光学脑成像无法触及的大脑区域。
