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3D motion strategy for online volumetric thermometry using simultaneous multi-slice EPI at 1.5T: an evaluation study
Valéry Ozenne1,2,3, Pierre Bour1,2,3, Baudouin Denis de Senneville4
1IHU Liryc, Electrophysiology and Heart Modeling Institute, Fondation Bordeaux Université, Pessac-Bordeaux, France.
Summary
This study introduces a faster 2D simultaneous multi-slice Echo Planar Imaging (EPI) sequence with multiband acceleration to improve temperature mapping accuracy during MR-guided thermotherapy, especially for mobile organs. The enhanced sequence achieves 2°C accuracy, increasing procedural safety.
Area of Science:
- Medical Imaging
- Physics in Medicine
- Interventional Radiology
Background:
- Respiratory motion significantly impacts temperature mapping accuracy in Magnetic Resonance Imaging (MRI) due to tissue displacement and phase variations.
- Fast 2D Echo Planar Imaging (EPI) can mitigate intra-scan motion, but inter-scan motion during free-breathing acquisition remains a challenge, leading to positional offsets between slices.
Purpose of the Study:
- To evaluate a 2D simultaneous multi-slice EPI sequence with multiband (MB) acceleration for improved temperature mapping during MR-guided radiofrequency ablation.
- To assess the impact of MB acceleration on inter-scan motion, temperature uncertainty, false-positive heating, and measurement repeatability.
- To implement and evaluate a 3D motion compensation pipeline to address through-plane motion.
Main Methods:
- A 2D simultaneous multi-slice EPI sequence with MB acceleration was tested on a mobile gel phantom and in a volunteer's liver.
- The sequence's performance was analyzed regarding inter-scan motion, temperature uncertainty, and repeatability.
- A 3D motion compensation pipeline was developed and applied to mitigate through-plane motion.
Main Results:
- In-plane motion was effectively compensated across all MB factors, with temperature distributions agreeing between heating and cooling phases.
- No significant false-positive heating was detected under the tested conditions.
- Repeatability yielded a 95% uncertainty below 2°C for MB1 and MB2, while MB3 showed higher uncertainty (up to 4.5°C) with aliasing artifacts.
- The combination of fast simultaneous multi-slice EPI and 3D motion compensation effectively reduced residual out-of-plane motion.
Conclusions:
- Volumetric temperature imaging with 2°C accuracy is achievable in under 700ms for 12 slices, offering flexibility in acquisition time or volume coverage.
- This approach enhances safety in MR-guided thermotherapy by enabling faster monitoring of larger volumes in mobile organs.
