A Magnetic Resonance Fingerprinting Approach for Simultaneous T 1 - and PRFS-Based 3D MR-Thermometry

To evaluate a three dimensional dual echo magnetic resonance fingerprinting sequence for simultaneous proton resonance frequency shift (PRFS) and $T_1$ thermometry during microwave ablation with $T_1$ improving robustness near gas bubble induced susceptibility changes while PRFS provides high precision elsewhere.

An ex vivo bovine liver was heated at 40 W for 8 min. A 3D stack-of-spiral FLASH-MRF acquisition on a 3 T system produced simultaneous PRFS- and $T_1$ -based thermometry. Two fiber optic probes served as references. $T_1$ was calibrated to temperature using a parenchymal region in PRFS thermometry. Thermal dose was computed as CEM43 and compared with post-cooling inversion-recovery imaging.

The $T_1$ -temperature slope was $4.81\mathrm{ms}/°C$ . In non-heated parenchyma, temporal standard deviation was $0.5\pm 0.2°C$ for PRFS and $1.3\pm 0.2°C$ for $T_1$ . At probe 1, RMSE was $0.9°C$ for PRFS and $2.2°C$ for $T_1$ . At a susceptibility-prone probe, PRFS RMSE was $15.3°C$ while $T_1$ RMSE was $2.1°C$ regarding only time points up to a CEM43 threshold of 240 min. Dose maps achieved Dice overlap of 67.13% for PRFS and 73.80% for $T_1$ .

A single three dimensional MRF acquisition provided complementary temperature information. PRFS delivered high precision where phase was stable. $T_1$ remained monotonic near susceptibility and improved dose overlap. The framework encoded $B_1^{+}$ and enabled in-session $T_1$ calibration from PRFS.