Free hydroxyl radical dosimetry by using 1 MHz low level ultrasound waves

Background : In order to quantify effects of ultrasound irradiation parameters under therapeutic condition, especially sonodynamic therapy, it is initially necessary to evaluate inertial cavitation activity in vitro conditions therefore, in this study, the effect of 1 MHz low level ultrasound based on °OH radicals generated by acoustic inertial cavitation in aqueous solution was monitored by their reaction with terephthalic acid (TA) to produce fluorescent 2-Hydroxyterephthalate acid (HTA) by spectrofluorometry method (Terephtalic acid dosimetry). Materials and Methods: The study was designed to measure hydroxyl radicals in a field near to 1 MHz sonotherapy probe in progressive mode and low level intensity. The effect of ultrasound irradiation parameters (1MHz) containing duty factor, mode, intensity ultrasound and, time sonication in hydroxyl radical production have been considered. After preparation of solution of dosimetry and plotting calibration curve of spectrofluorescence, the effect of mode of sonication (continuous and pulsating), duty factor (20-80%), intensity (0-2 W/cm2, with step of 0.5 W/cm2), and sonication time (0-60min with step time of 10min) without increasing temperature to more than 3°C to determine the effective exposure in low level ultrasound were evaluated. The fluorescence intensity of TA solution before and after irradiation, in all cases was measured, and the results were reported as Mean ± Standard Deviation (SD). Result : The result of experiments related to sonication mode for 1MHz ultrasound irradiation (2 W/cm2) show that continuous mode of sonication is 29% higher fluorescence intensity than the pulse mode in 80% duty cycle for sonodynamic therapy. With compensation of irradiation time for 1MHz sonication in different duty cycles, fluorescence intensity in continuous mode is 22% higher than the pulse mode in average. The amount of hydroxyl radicals production versus ultrasound intensity, and sonication time show with increasing intensity or sonication time in continuous mode, the hydroxyl radical production is linearity increased (R=0.99). Conclusion: The results show that the terephthalic acid dosimetry is suitable for detecting and quantifying free hydroxyl radical as a criterion of inertial cavitation production over a range of condition in medical ultrasound fields.