Guillen Alexander R, Truong Dennis Q, Faria Paula Cristina, Pryor Brian, de Taboada Luis, Datta Abhishek
Research and Development, Soterix Medical, Woodbridge, NJ, USA.
Mathematics Department, Polytechnic University of Leiria, Leiria, Portugal.
Neuromodulation. 2025 Jul 25. doi: 10.1016/j.neurom.2025.06.003.
Transcranial photobiomodulation (tPBM) is the noninvasive application of light to modulate underlying brain activity. There is increasing interest in evaluating tPBM as a therapeutic option. The typical technological questions are extent of light penetration and associated tissue temperature increases. Limited computational efforts to quantify these aspects are restricted to simplified models.
We considered a three-dimensional high-resolution (1 mm) anatomically realistic head model to simulate tPBM with the light source targeting the F3 region at 800 nm wavelength. Power densities spanning three decades (10, 100, and 1000) mW/cm were investigated. We also tested time-variant application at 100 mW/cm for up to 20 minutes. Finally, tissue temperature increases for the American National Standards Institute safety limit of 330 mW/cm also were determined at a test case.
Our predictions reveal that the induced cortical irradiance is largely focal, demarcated by the shape and extent of the source. Approximately 1% of the injected irradiance reaches the gray matter. Aligned with previous efforts, the scalp accounts for the greatest loss (∼65%). The irradiance reduces to a hundredth of the value from gray matter at an approximately 113-mm perpendicular distance from its surface. There is a growing halo-like effect at the level of cerebrospinal fluid (CSF), which is extended down to the underlying cortex. The CSF was found to be mainly responsible for this effect. We observe scalp temperature increases of 0.38 °C and 3.76 °C for 100 and 1000 mW/cm power density, respectively. The corresponding brain temperature increases are predicted to be 0.06 °C and 0.57 °C. As expected, irradiance absorption is linear with applied power density. Although the maximum induced scalp temperature increases linearly with power density, maximum brain temperature increases less slowly with power density. Transient analysis at 100 mW/cm power density indicates expected scalp temperature increase with increasing stimulation duration. Temperature increases asymptote in approximately 10 minutes.
tPBM presents unique potential to directly impose a desired spatial profile using simple alteration of the shape and size of the source. Usage of power density of 1000 mW/cm exceeds scalp and brain temperature safety limits. Contrary to prior reports, light penetration can exceed >10 cm from gray matter surface.
经颅光生物调节（tPBM）是一种通过非侵入性地应用光来调节大脑深层活动的方法。人们对将tPBM作为一种治疗选择的评估兴趣日益浓厚。典型的技术问题包括光穿透的程度以及相关的组织温度升高。用于量化这些方面的有限计算工作仅限于简化模型。
我们考虑了一个三维高分辨率（1毫米）的解剖学逼真头部模型，以模拟tPBM，光源波长为800纳米，靶向F3区域。研究了跨越三个数量级（10、100和1000）毫瓦/平方厘米的功率密度。我们还测试了在100毫瓦/平方厘米下长达20分钟的时变应用。最后，在一个测试案例中确定了美国国家标准协会330毫瓦/平方厘米安全限值下的组织温度升高情况。
我们的预测表明，诱导的皮质辐照度在很大程度上是局部性的，由光源的形状和范围界定。注入辐照度的约1%到达灰质。与之前的研究一致，头皮造成的损失最大（约65%）。在距灰质表面约113毫米的垂直距离处，辐照度降至灰质处值的百分之一。在脑脊液（CSF）水平出现越来越明显的晕轮效应，并延伸至下方的皮质。发现CSF对此效应起主要作用。我们观察到，对于100和1000毫瓦/平方厘米的功率密度，头皮温度分别升高0.38℃和3.76℃。预计相应的大脑温度升高分别为0.06℃和0.57℃。正如预期的那样，辐照度吸收与施加的功率密度呈线性关系。虽然最大诱导头皮温度随功率密度呈线性增加，但最大大脑温度随功率密度增加的速度较慢。在100毫瓦/平方厘米功率密度下的瞬态分析表明，随着刺激持续时间的增加，头皮温度会升高。温度升高在大约10分钟内渐近。
tPBM具有独特的潜力，可通过简单改变光源的形状和大小直接施加所需的空间分布。1000毫瓦/平方厘米的功率密度使用超过了头皮和大脑温度安全限值。与先前的报告相反，光穿透可超过灰质表面10厘米以上。
