Color-Changing Reflection Hologram for Quality Assurance of Therapeutic Ultrasound Systems

The acoustic outputof clinical therapeutic ultrasound equipmentrequires regular quality assurance (QA) testing to ensure the safetyand efficacy of the treatment and that any potentially harmful deviationsfrom the expected output power density are detected as soon as possible.A hologram, consisting of a reflection grating fabricated in an acrylate photopolymerfilm, has been developed to produce an immediate, visible, and permanentchange in the color of the reconstructed hologram from red to greenin response to incident ultrasound energy. The influence of the therapeuticultrasound insonation parameters (exposure time, ultrasound powerdensity, and proximity to the point of maximum acoustic pressure)on the hologram's response has been investigated for two typesof therapeutic ultrasound systems: a sonoporation system and an ultrasoundphysiotherapy system. Findings show that, above a switching temperatureof 45 & DEG;C, the ultrasound-induced temperature rise produces astructural change in the hologram, which manifests as a visible colorchange. The area of the color change region correlates with the ultrasoundexposure conditions. The suitability of the hologram as a simple andquick QA test tool for therapeutic ultrasound systems has been demonstrated.A prototype ultrasound testing unit which facilitates user-friendly,reproducible testing of the holograms in a clinical setting is alsoreported.