title: Ultrasonography-based 2D motion-compensated HIFU sonication integrated with reference-free MR temperature monitoring: a feasibility study ex vivo.
abstract: Magnetic resonance imaging (MRI) and ultrasonography have been used simultaneously in this ex vivo study for the image-guidance of high intensity focused ultrasound (HIFU) treatment in moving tissue. A ventilator-driven balloon produced periodic and non-rigid (i.e. breathing-like) motion patterns in phantoms. MR-compatible ultrasound (US) imaging enabled near real-time 2D motion tracking based on optical flow detection, while near-harmonic reference-free proton resonance frequency shift (PRFS) MR thermometry (MRT) was used to monitor the thermal buildup on line. Reference-free MRT was applied to gradient-echo echo-planar imaging phase maps acquired at the frame rate of 250 to 300 ms/slice with voxel size 1.25×1.25×5 mm(3). The MR-US simultaneous imaging was completely free of mutual interferences while minor RF interferences from the HIFU device were detected in the far field of the US images. The effective duty-cycle of the HIFU sonication was close to 100 % and no off-interval was required to temporally decouple it from the ultrasonography. The motion compensation of the HIFU sonication was achieved with an 8 Hz frame rate and sub-millimeter spatial accuracy, both for single-focus mode and for an iterated multi-foci line scan. Near harmonic reference-less PRFS MRT delivered motion-robust thermal maps perpendicular or parallel to the HIFU beam (0.7 °C precision, 0.5 °C absolute accuracy). Out-of-plane motion compensation was not addressed in this study.
authors.affiliation: Faculty of Medicine, University of Geneva, Switzerland.
authors.forename: Vincent
authors.initials: V
authors.lastname: Auboiroux
authors.forename: Lorena
authors.initials: L
authors.lastname: Petrusca
authors.forename: Magalie
authors.initials: M
authors.lastname: Viallon
authors.forename: Thomas
authors.initials: T
authors.lastname: Goget
authors.forename: Christoph D
authors.initials: CD
authors.lastname: Becker
authors.forename: Rares
authors.initials: R
authors.lastname: Salomir
mesh_terms: D005240:Feasibility Studies; D057086:High-Intensity Focused Ultrasound Ablation / Q000295:instrumentation / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009068:Movement; D019047:Phantoms, Imaging; D013010:Sonication / Q000379:methods*; D018511:Systems Integration; D013696:Temperature; D014463:Ultrasonography / Q000379:methods*