Motion correction in MR thermometry of abdominal organs: a comparison of the referenceless vs. the multibaseline approach.

Reliable temperature and thermal-dose measurements using proton resonance frequency shift-based magnetic resonance (MR) thermometry for MR-guided ablation of abdominal organs require a robust correction of artefacts induced by the target displacement through an inhomogeneous and time-variant magnetic field. Two correction approaches emerged recently as promising candidates to allow continuous real-time MR-thermometry under free-breathing conditions: The multibaseline correction method, which relies on a pre-recorded correction table allowing to correct for periodic phase changes, and the referenceless method, which depends on a background phase estimation in the target area based on the assumption of a smooth spatial variation of the phase across the organ. This study combines both methods with real-time in-plane motion correction to permit both temperature and thermal-dose calculations on the fly. Subsequently, the practical aspects of both methods are compared in two application scenarios, a radio frequency-ablation and a high-intensity focused ultrasound ablation. A hybrid approach is presented that exploits the strong points of both methods, allowing accurate and precise proton resonance frequency-thermometry measurements during periodical displacement, even in the presence of spontaneous motion and strong susceptibility variations in the target area.