Thermal impact of near-infrared laser in advanced noninvasive optical brain imaging

Abstract

The propagation of laser light in human tissues is an important issue in functional optical imaging. We modeled the thermal effect of different laser powers with various spot sizes and different head tissue characteristics on neonatal and adult quasirealistic head models. The photothermal effect of near-infrared laser (800 nm) was investigated by numerical simulation using finite-element analysis. Our results demonstrate that the maximum temperature increase on the brain for laser irradiance between 0.127 (1 mW) and [Formula: see text] (100 mW) at a 1 mm spot size, ranged from 0.0025°C to 0.26°C and from 0.03°C to 2.85°C at depths of 15.9 and 4.9 mm in the adult and neonatal brain, respectively. Due to the shorter distance of the head layers from the neonatal head surface, the maximum temperature increase was higher in the neonatal brain than in the adult brain. Our results also show that, at constant power, spot size changes had a lesser heating effect on deeper tissues. While the constraints for safe laser irradiation to the brain are dictated by skin safety, these results can be useful to optimize laser parameters for a variety of laser applications in the brain. Moreover, combining simulation and adequate in vitro experiments could help to develop more effective optical imaging to avoid possible tissue damage.

Direct monitoring of light mediated hyperthermia induced within mammalian tissues using surface enhanced spatially offset Raman spectroscopy (T-SESORS)

“…This increase in temperature is attributed to general photothermal interaction of the laser with tissue constituents e.g. water absorption of the illumination beam, 28,29 and not significantly due to the nanoparticles, as previously it was shown there was minimal increase in temperature of the nanoparticles alone with the same power (Fig. 1B).…”

Laser safety in fiber-optic monitoring of spinal cord hemodynamics: a preclinical evaluation

“…The computational results (10 mW at 100% duty cycle) that most closely resemble the work described (i.e., 27 mW at 35% duty cycle) suggest that laser illumination could potentially induce a highly localized 1.5°C increase in temperature. 59 However, our experimental results using thermometry did not demonstrate such a change in the spinal cord with the illumination parameters described above, despite our thermal experiment occurring in a worst-case scenario of zero blood flow (excised tissue). We note that the catheter wall in our probe is ∼0.4-mm thick and the beam exiting the fiber-optic is diverging (0.22 NA), both of which serves to minimize localized heating effects.…”

Living optical random neural network with three dimensional tumor spheroids for cancer morphodynamics

“…We first consider glioblastoma 3DTM that are chemically fixed (see "Methods") and do not evolve with time, and we demonstrate morphology alterations by inducing hyperthermia. Infrared (IR) laser-induced temperature variations in brain tissue are studied in many applications, such as imaging and cancer therapy 36,37 . There are several open questions concerning the temperature response in cell assemblies.…”