Application of a Temperature-Dependent Fluorescent Dye (Rhodamine B) to the Measurement of Radiofrequency Radiation-Induced Temperature Changes in Biological Samples

We have applied a non-contact method for studying the temperature changes produced by radiofrequency (RF) radiation specifically to small biological samples. A temperature-dependent fluorescent dye, Rhodamine B, as imaged by laser scanning confocal microscopy (LSCM) was used to do this. The results were calibrated against real-time temperature Measurements from fiber optic probes, with a calibration factor of 3.4% intensity change degrees C-1 and a reproducibility of +/- 6%. This non-contact method provided two-dimensional and three-dimensional images of temperature change distributions in biological samples, at a spatial resolution of a few micrometers and with all estimated absolute precision of around 1.5 degrees C, with a differential precision of 0.4 degrees C. Temperature rise within tissue was found to be non-uniform. Estimates of specific absorption rate (SAR) from absorbed power measurements were greater than those estimated from rate of temperature rise, measured at 1 min intervals, probably because this interval is too long to permit accurate estimation of initial temperature rise following start of RF exposure. Future experiments will aim to explore this. Bioelectromagnetics 30:583-590, 2009. (C) 2009 Wiley-Liss. Inc.