Abstract
The thermal effect may be a desired outcome or a concerning side effect in laser-tissue interactions. Research in this area is particularly motivated by recent advances in laser applications in diagnosis and treatment of neurological disorders. Temperature as a side effect also limits the maximum power of optical transfer and harvesting of energy in implantable neural prostheses. The main objective was to investigate the thermal effect of a near-infrared laser beam directly aimed at the brain cortex. A small, custom-made thermal probe was inserted into the rat brain to make direct measurements of temperature elevations induced by a free-air circular laser beam. The time dependence and the spatial distribution of the temperature increases were studied and the maximum allowable optical power was determined to be 2.27 W/cm2 for a corresponding temperature increase of 0.5°C near the cortical surface. The results can be extrapolated for other temperature elevations, where the margin to reach potentially damaging temperatures is more relaxed, by taking advantage of linearity. It is concluded that the thermal effect depends on several factors such as the thermal properties of the neural tissue and of its surrounding structures, the optical properties of the particular neural tissue, and the laser beam size and shape. Because so many parameters play a role, the thermal effect should be investigated for each specific application separately using realistic in vivo models.
Highlights
Near-infrared (NIR) light finds applications in medicine for diagnostic and therapeutic purposes such as spectroscopic imaging[1] and the treatment of brain tumors.[2]
We experimentally found the scattering coefficient to be around 108 cm–1 in the rat brain gray matter.[15]
The noteworthy outcome is that the significant levels of optical energy (2.27 mW∕ mm2) can be injected into the brain tissue before the thermal effect reaches a critical level that may influence the homeostasis of the local neurons
Summary
Near-infrared (NIR) light finds applications in medicine for diagnostic and therapeutic purposes such as spectroscopic imaging[1] and the treatment of brain tumors.[2]. Microelectrode arrays often fail due to breakage of wire interconnects and the chronic tissue response caused by the tethering forces of the wires
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
