Endocavitary Phased Array Applicator of Therapeutic Ultrasound with an Integrated Opposed-Solenoid Coil for High Resolution MRI-Guided Thermotherapy: An in Vivo Study

Mihaela Rata^1,2, Francois Cotton^3,4, Christian Paquet⁵, Vlad Birlea¹, Michael Bock⁶, Rares Salomir¹

High intensity contact ultrasound (HICU) under MRI guidance may provide minimally invasive treatment of endocavitary digestive tumors (colon/rectum). In this study, opposed-solenoid receiver-only coils were integrated into an endoscopic phased array ultrasound probe to offer high resolution MRI guidance of thermotherapy. The improvement of the image quality and temperature monitoring and control using this device has been investigated in- vivo, on a clinical 1.5T. The comparison endocavitary/external standard coils (voxel: 0.88 x 0.88 x 8 mm³) showed a sensitivity gain up to a factor 4, at the limit of the cooling balloon. Infra-millimeter resolution became feasible for fast MR thermometry while providing an excellent SDT. The endoscopic device was actively operated under automatic temperature control, demonstrating accurate performance.