3D-printed acoustic holograms to generate thermal holographic patterns

Abstract

3D-printed holographic lenses coupled to an ultrasound transducer shape the acoustic field into arbitrary images. Predefined thermal patterns can be created with this technology in absorbing media, which can be used to generate localized and specific hyperthermia treatments. In this work we study how non-linearities in the acoustic field can affect the produced thermal pattern at hyperthermia intensity powers. A ‘2'-shaped acoustic hologram was designed with time-reversal methods and both acoustic and thermal numerical simulations were performed considering linear and non-linear propagation of the resulting acoustic field in liver-like medium. Experimental validation of the acoustic hologram was performed in degassed water, while the corresponding thermal pattern was evaluated using magnetic resonance thermometry and infra-red imaging in ex-vivo cow liver tissue and tissue-mimicking phantom. Simulations and experiments were in complete agreement, demonstrating that at hyperthermia intensities most of the energy is carried by the fundamental frequency and thus nonlinear propagation have little impact on resulting thermal pattern.