SU‐E‐J‐04: Integration of Interstitial High Intensity Therapeutic Ultrasound Applicators On a Clinical MRI‐Guided High Intensity Focused Ultrasound Treatment Planning Software Platform

Abstract

Purpose:Interstitial high intensity therapeutic ultrasound (HITU) applicators can be used to ablate tissue percutaneously, allowing for minimally‐invasive treatment without ionizing radiation [1,2]. The purpose of this study was to evaluate the feasibility and usability of combining multielement interstitial HITU applicators with a clinical magnetic resonance imaging (MRI)‐guided focused ultrasound software platform.Methods:The Sonalleve software platform (Philips Healthcare, Vantaa, Finland) combines anatomical MRI for target selection and multi‐planar MRI thermometry to provide real‐time temperature information. The MRI‐compatible interstitial US applicators (Acoustic MedSystems, Savoy, IL, USA) had 1–4 cylindrical US elements, each 1 cm long with either 180° or 360° of active surface. Each applicator (4 Fr diameter, enclosed within a 13 Fr flexible catheter) was inserted into a tissue‐mimicking agar‐silica phantom. Degassed water was circulated around the transducers for cooling and coupling. Based on the location of the applicator, a virtual transducer overlay was added to the software to assist targeting and to allow automatic thermometry slice placement. The phantom was sonicated at 7 MHz for 5 minutes with 6–8 W of acoustic power for each element. MR thermometry data were collected during and after sonication.Results:Preliminary testing indicated that the applicator location could be identified in the planning images and the transducer locations predicted within 1 mm accuracy using the overlay. Ablation zones (thermal dose ≥ 240 CEM43) for 2 active, adjacent US elements ranged from 18 mm × 24 mm (width × length) to 25 mm × 25 mm for the 6 W and 8 W sonications, respectively.Conclusion:The combination of interstitial HITU applicators and this software platform holds promise for novel approaches in minimally‐invasive MRI‐guided therapy, especially when bony structures or air‐filled cavities may preclude extracorporeal HIFU.[1] Diederich et al. IEEE UFFFC 46.5 (1999): 1218.[2] Chopra et al. PMB 50.21 (2005): 4957.Funding support was provided by Philips Healthcare and in‐kind support from Acoustic MedSystems Inc. Ari Partanen is a paid employee of Philips Healthcare. Goutam Ghoshal and Everette Clif Burdette are paid employees of Acoustic MedSystems Inc.