The Sarvazyan method of mapping ultrasound fields

Ultrasound is used widely therapeutic medicine. The uses of ultrasound requires experimental methods to define the intensity distribution generated by the transducer or array of transducers. The method described by Sarvazyan et al (1985) is believed to be a simple and rapid method to achieve this objective. The field is directed through an aqueous solution of methylene blue dye at a sheet of white paper (Astralux 200 μm card). After, typically 1 minute exposure, the paper is withdrawn from the solution and the resulting pattern of dye on the paper maps the intensity distribution of ultrasound. The Sarvazyan method was attributed to an increased rate of diffusion of the dye into the paper caused by the vibration amplitude of the sound field generating enhanced diffusion of dye into the paper but the mode of action was not explained. The authors have subsequently examined the paper by optical and scanning electron microscopy. They have been able to show that microstreaming velocity is proportional to the (local) intensity of ultrasound on a surface