The efficacy of an ultrasound ring-array transducer for hyperthermia generation

In mild hyperthermia (MHTh), targeted tumors are heated to approximately 41 to 44°C, typically to enhance chemo-, radiation, and/or immunotherapy. This study demonstrates the efficacy of a ring-array ultrasound (US) transducer in generating and monitoring MHTh in heterogeneous media. A ring-array provides enhanced focusing and heat localization compared to conventional linear-array US. We simulated scenarios using either one, two, or four 128-element linear-array transducers, or a 256-element ring-array transducer, to generate focused US profiles. The full width half maximum (FWHM) was measured to quantify the results. The ring-array achieved the most accurate and localized focal pressure profile with a focal spot size of 2×2mm. In a simulated heterogeneous breast model, sound speed (SS) compensation with a ring-array resulted in more efficient acoustic focusing than non-compensated fields. The focal point without SS compensation shifted spatially from its target due to acoustic aberrations, highlighting the importance of aberration correction for precise heat localization. Additionally, the ring-array's heat generation capability was evaluated in-vitro using a tissue-mimicking phantom, where the temperature at the focal point was increased by 6°C in 12 minutes and was sustainable. Lastly, the capability of a ring-array to track temperature was evaluated using US tomography (UST) in another in-vitro experiment. Here, a cylindrical inclusion in a tissue-mimicking phantom was filled with preheated water and allowed to passively cool from 45°C to 25°C. A ring-array tracked the temperature changes based on SS images with a mean error of 0.06±0.28°C. In summary, a ring-array transducer (1) achieved the best focal profile compared to standard linear transducers, (2) accomplished superior aberration correction using SS images, resulting in better aberration-free focusing in heterogeneous media, (3) generated sustainable heat at a focal point, and (4) accurately monitored temperature changes with UST.