In Vivo 3D Hybrid fat-water MR Thermometry via Simultaneous Proton Resonance Frequency Shift and T1 Measurement

Motivation: In current clinical magnetic resonance-guided focused ultrasound (MRgFUS) ablation applications, only aqueous tissues are monitored with MR thermometry. Accurate thermometry of heterogeneous aqueous and fat tissue volumes would increase treatment safety and efficacy. Goal(s): Evaluate a single reference variable flip angle (SR-VFA) sequence for hybrid proton resonance frequency shift and ΔT1 MR thermometry in heterogeneous tissue volumes. Approach: MRgFUS ablation in an in vivo rabbit model was monitored with SR-VFA thermometry. Cumulative thermal dose (CTD) maps calculated from SR-VFA images were compared with non-perfused volumes and histological samples. Results: SR-VFA derived CTD maps accurately predicted volumes of thermal damage in muscle and fat. Impact: Hybrid proton resonance frequency shift and T1 thermometry allows for accurate temperature monitoring of heterogeneous tissue volumes. This increases the safety and efficacy of MR-guided focused ultrasound treatments in mixed-tissue treatment areas by ensuring target temperatures reach appropriate thresholds.