title: ARFI-prepared MRgHIFU in liver: simultaneous mapping of ARFI-displacement and temperature elevation, using a fast GRE-EPI sequence.
abstract: MR acoustic radiation force imaging (ARFI) is an elegant adjunct to MR-guided high intensity focused ultrasound for treatment planning and optimization, permitting in situ assessment of the focusing and targeting quality. The thermal effect of high intensity focused ultrasound pulses associated with ARFI measurements is recommended to be monitored on line, in particular when the beam crosses highly absorbent structures or interfaces (e.g., bones or air-filled cavities). A dedicated MR sequence is proposed here, derived from a segmented gradient echo-echo planar imaging kernel by adding a bipolar motion encoding gradient with interleaved alternating polarities. Temporal resolution was reduced to 2.1 s, with in-plane spatial resolution of 1 mm. MR-ARFI measurements were executed during controlled animal breathing, with trans-costal successively steered foci, to investigate the spatial modulation of the focus intensity and the targeting offset. ARFI-induced tissue displacement measurements enabled the accurate localization, in vivo, of the high intensity focused ultrasound focal point in sheep liver, with simultaneous monitoring of the temperature elevation. ARFI-based precalibration of the focal point position was immediately followed by trans-costal MR-guided high intensity focused ultrasound ablation, monitored with a conventional proton resonance frequency shift MR thermometry sequence. The latter MR thermometry sequence had spatial resolution and geometrical distortion identical with the ARFI maps, hence no coregistration was required.
authors.affiliation: Faculty of medicine, University of Geneva, Geneva, Switzerland. vincent.auboiroux@unige.ch
authors.forename: Vincent
authors.initials: V
authors.lastname: Auboiroux
authors.forename: Magalie
authors.initials: M
authors.lastname: Viallon
authors.forename: Joerg
authors.initials: J
authors.lastname: Roland
authors.forename: Jean-Noël
authors.initials: JN
authors.lastname: Hyacinthe
authors.forename: Lorena
authors.initials: L
authors.lastname: Petrusca
authors.forename: Denis R
authors.initials: DR
authors.lastname: Morel
authors.forename: Thomas
authors.initials: T
authors.lastname: Goget
authors.forename: Sylvain
authors.initials: S
authors.lastname: Terraz
authors.forename: Patrick
authors.initials: P
authors.lastname: Gross
authors.forename: Christoph D
authors.initials: CD
authors.lastname: Becker
authors.forename: Rares
authors.initials: R
authors.lastname: Salomir
mesh_terms: D000818:Animals; D001831:Body Temperature; D054459:Elasticity Imaging Techniques / Q000379:methods*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005260:Female; D057086:High-Intensity Focused Ultrasound Ablation / Q000379:methods*; D008099:Liver / Q000033:anatomy & histology / Q000502:physiology* / Q000601:surgery*; D012756:Sheep; D025321:Surgery, Computer-Assisted / Q000379:methods*; D013817:Thermography / Q000379:methods*