ESR dosimetry of free radicals-a comparison between high intensity ultrasound fields and an ionizing Cs137 source

High intensity ultrasound fields have the potential to produce free radicals in aqueous solutions caused by inertial cavitation. In this study we compared the production of free radicals under different sonication modalities with radical formation in the field of a well known Cs¹³⁷ gamma-ray source. In addition we examined the enhancement of radical production by photodynamic substances. Analysis of radical formation was performed with an ESR spectrometer. Sonication of aqueous test solution was carried out with high intensity focused ultrasound (HIFU) and with an unfocused ultrasound field in a standing wave mode against a solution/air interface. We were able to assess the quantity of free radicals developing in photon field as well as in US fields. It was feasible to determine equivalent dose values comparing ultrasound with photon irradiation. A significant enhancement of radical production by a photosensitizer was only detected in the unfocused ultrasound field in a standing wave mode