Assessment of heating effects in skin during continuous wave near infrared spectroscopy

Abstract

Near infrared spectroscopy is an increasingly important tool for the investigation of human brain function, however, to date there have been few systematic evaluations of accompanying thermal effects due to absorption. We have measured the spatial distribution of temperature changes during near infrared irradiation (789 nm) as a function of laser power, in both excised tissue (chicken meat and skin) and in the forearm of an awake human volunteer. Light was applied using a 1 mm optical fiber which is characteristic of the topographic system. The temperature of excised chicken tissue increased linearly with power level as 0.097 and 0.042 degrees C/mW at depths of 0 and 1 mm, respectively. Human forearm studies yielded temperature changes of 0.101, 0.038, and 0.030 degrees C/mW at depths of 0.5, 1.0, and 1.5 mm, respectively. Due to direct irradiation of the thermocouple all measurements represent the maximum temperature increase from the laser. In all cases the estimated heating effects from continuous wave optical topography systems were small and well below levels which would endanger tissue cells. The close similarity between ex vivo and in vivo measurements suggests negligible contributions from blood flow in the skin which was further supported by measurements during cuff ischemia. Heating effects decreased sharply with both depth and lateral position; thus, for optode spacings greater than a few millimeters, fibers can be treated independently. Finite element analysis confirms that the experimental results are consistent with a simple heat conduction model.

A review on continuous wave functional near-infrared spectroscopy and imaging instrumentation and methodology

“…However, certain limitations apply. Tissue heating due to the irradiation and/or conductive heat transport from the source not only may distort the measurements, but may endanger or at least cause discomfort to the subject (Bozkurt and Onaral, 2004;Ito et al, 2000;Soraghan et al, 2008). More important, however, is proper safety for the eyes, for both, the experimenter and the subject.…”

Synchronous activity of two people's prefrontal cortices during a cooperative task measured by simultaneous near-infrared spectroscopy

“…[30][31][32][33] On the basis of NIRS, optical topography (OT), 34,35 which uses multiple light sources and detectors, obtains two-dimensional topographical images of the changes in cerebral blood volume. OT systems have been widely used for research and clinical purposes, [36][37][38][39][40] especially for measuring the brain activity of infants and children, 25, 41-45 because they have a high level of safety 46,47 and require few constraints. For simultaneously measuring of multiple participants' brains (i.e., hyperscanning) and thereby investigating the relationship between brain activity and social interaction, some researchers used EEG, [48][49][50][51] which is less expensive and has a higher temporal resolution than NIRS.…”

Dynamic phantom with two stage-driven absorbers for mimicking hemoglobin changes in superficial and deep tissues

“…This technique has been widely used in research related to language 9 and infants 10,11 as well as for clinical purposes 12,13 due to its advantageous features, which include noninvasiveness, 14,15 low constraint, and portability. [16][17][18] In this technique, the scalp is irradiated with near-infrared light, and the light that is propagated in and scattered from the tissue is detected at another position.…”