3D MR Thermometry Using Bi-Directional Segmented EPI for Transcranial-Focused Ultrasound

Area of Science:

• Magnetic Resonance Imaging
• Medical Physics
• Thermal Therapy Monitoring

Background:

• Clinical 2D thermometry is the standard for monitoring thermal therapies.
• Limitations exist in 2D thermometry regarding accuracy and spatial coverage.
• Advancements in MRI sequences may offer improved thermometry solutions.

Purpose of the Study:

• To assess the feasibility of replacing 2D thermometry with 3D segmented EPI-based thermometry (segEPI).
• To evaluate if 3D segEPI achieves equivalent accuracy, precision, and scan time.
• To determine the potential for rapid clinical integration of 3D segEPI.

Main Methods:

• Modified a 3D segEPI sequence for bidirectional readouts.
• Integrated the modified sequence into a clinical protocol.
• Performed focused ultrasound sonication in phantoms and in vivo scans to compare 3D segEPI with 2D thermometry, analyzing accuracy, precision, and heating extent at various interpolation levels.

Main Results:

• 3D segEPI demonstrated high agreement with 2D clinical thermometry.
• Temperature agreement remained within ±1°C with 0.5 mm in-plane voxel spacing.
• 3D segEPI provided better characterization of heating distribution, though with a slightly wider full-width at half maximum (∼17%).
• Echo combination in segEPI improved temperature estimate precision.

Conclusions:

• 3D segEPI thermometry is a viable and promising alternative to current 2D clinical methods.
• The technique shows potential for seamless integration into existing clinical workflows.
• 3D segEPI enhances the monitoring of thermal therapies with improved spatial information.