Multi-echo gradient echo pulse sequences: which is best for PRFS MR thermometry guided hyperthermia?

Area of Science:

• Medical Imaging
• Biophysics
• Radiology

Background:

• MR thermometry (MRT) is crucial for noninvasive temperature monitoring during hyperthermia therapies.
• Clinical MRT is established in the abdomen and extremities, with head-region devices under development.
• Optimizing MRT across all anatomical areas requires selecting the best sequence setup and post-processing for demonstrated accuracy.

Purpose of the Study:

• To compare the performance of the traditional double-echo gradient-echo (DE-GRE) sequence with multi-echo (ME) sequences for MR thermometry.
• To evaluate the accuracy of different MR thermometry sequences in phantom and volunteer studies.
• To identify the most promising sequence for clinical hyperthermia applications.

Main Methods:

• Compared DE-GRE (2 echoes, 2D) with ME-FGRE (11 echoes, 2D) and 3D-ME-FGRE (11 echoes, 3D) sequences on a 1.5T MR scanner.
• Assessed performance using a phantom cooling from 59°C to 34°C and unheated volunteer brains (n=10).
• Utilized multi-peak fitting for off-resonance frequency calculation and automatic internal body fat selection for B0 drift correction.

Main Results:

• The 3D-ME-FGRE sequence achieved higher accuracy: 0.20°C in phantom and 0.75°C in volunteers.
• Traditional DE-GRE showed lower accuracy: 0.37°C in phantom and 1.96°C in volunteers.
• In-plane motion was compensated using rigid body image registration.

Conclusions:

• The 3D-ME-FGRE sequence is the most promising candidate for hyperthermia applications due to its superior accuracy.
• The multi-echo nature allows automatic B0 drift correction using internal body fat, a key feature for clinical use.
• This sequence enhances the reliability and applicability of MR thermometry in diverse anatomical regions.