Multi-purpose robotic system of therapeutic ultrasound guided by magnetic resonance imaging

Abstract

High Intensity Focus Ultrasound (HIFU) can offer completely non invasive or minimally invasive therapies for various diseases while sparing intervenient tissue. Furthermore Magnetic Resonance Imaging (MRI) can provide well defined margins between tumors and healthy tissue as well as the ability of monitoring the tissue temperature. HIFU can also be used to induce high temperatures hence, it can be utilized to ablate malignant tumors in various organs. In this study the main objective was the development of MR safe robotic systems to maneuver HIFU transducer in five degrees of freedom (3 linear, 2 angular). The range of motion is up to 14 cm for the linear axis and 180̊ for the angular axis. Optical encoders enable motion accuracy of 20 μm. The positioning devices incorporate only MRI compatible materials and are small enough to fit in most commercial MRI scanners. The robotic systems were tested successfully in phantoms and freshly excised tissue in various tasks (robot motion, MR compatibility, and MR thermometry). With minimum changes these robotic systems can be converted into devices for performing interventions with focused ultrasound in various human organs. Due to the heating in the pre-focal field the delay between successive movements in HIFU are sometimes as long as 60 s, resulting to treatment time in the order of 2-3 h. To reduce the treatment time alternative transducer motion algorithms explored in order to reduce pre-focal heating and treatment time. The simulations suggest that it is possible to reduce the treatment time up to 93 %. Therefore, it will be possible to achieve treatment time of focused ultrasound therapies shorter than 30 min.