Temperature Mapping During MR-Guided Cryoablation Using a FLORET UTE Sequence.

Area of Science:

• Medical Imaging
• Biophysics
• Interventional Radiology

Background:

• Accurate temperature monitoring is crucial for effective cryoablation.
• Existing MR thermometry methods often lack the speed required for real-time guidance during cryoablation procedures.

Purpose of the Study:

• To develop and validate a 3D Fast Low-angle Optimized Rapid Echo Train (FLORET)-simultaneous multi-slice (SMS) Echo Planar Imaging (EPI) sequence for rapid MR thermometry.
• To assess the accuracy of this sequence in mapping temperatures during cryoablation in ex vivo liver tissue.

Main Methods:

• A 3D FLORET-UTE sequence with a 1.6 mm isotropic resolution and 18-second acquisition time was implemented on a 3T scanner.
• Cryoablation was performed on ex vivo bovine liver phantoms, with temperatures monitored by fiber-optic probes.
• MR images were reconstructed using l2-regularized non-Cartesian SENSE, and temperature accuracy was evaluated using RMSE and Bland-Altman analysis.

Main Results:

• A strong correlation (R²=0.95) was observed between MR signal and temperature.
• Prospective validation showed root-mean-square errors between 0.93°C and 1.73°C (overall 1.33°C).
• The technique captured 3D ice-ball dynamics with 18-second temporal resolution, significantly faster than previous UTE methods.

Conclusions:

• The FLORET-UTE sequence enables quantitative 3D MR thermometry of frozen tissue with sub-20-second temporal resolution and sub-2°C accuracy.
• This technique overcomes speed limitations of earlier UTE methods and shows promise for real-time MR-guided cryoablation.
• Further in vivo evaluation is warranted to confirm its clinical utility.