Hybrid ultrasound-MR guided HIFU treatment method with 3D motion compensation

Purpose : Treatments using high‐intensity focused ultrasound (HIFU) in the abdominal region remain challenging as a result of respiratory organ motion. A novel method is described here to achieve 3D motion‐compensated ultrasound (US) MR‐guided HIFU therapy using simultaneous ultrasound and MRI. Methods : A truly hybrid US‐MR‐guided HIFU method was used to plan and control the treatment. Two‐dimensional ultrasound was used in real time to enable tracking of the motion in the coronal plane, whereas an MR pencil‐beam navigator was used to detect anterior–posterior motion. Prospective motion compensation of proton resonance frequency shift (PRFS) thermometry and HIFU electronic beam steering were achieved. Results : The 3D prospective motion‐corrected PRFS temperature maps showed reduced intrascan ghosting artifacts, a high signal‐to‐noise ratio, and low geometric distortion. The k‐space data yielded a consistent temperature‐dependent PRFS effect, matching the gold standard thermometry within approximately 1°C. The maximum in‐plane temperature elevation ex vivo was improved by a factor of 2. Baseline thermometry acquired in volunteers indicated reduction of residual motion, together with an accuracy/precision of near‐harmonic referenceless PRFS thermometry on the order of 0.5/1.0°C. Conclusions : Hybrid US‐MR‐guided HIFU ablation with 3D motion compensation was demonstrated ex vivo together with a stable referenceless PRFS thermometry baseline in healthy volunteer liver acquisitions