In vivo simultaneous proton resonance frequency shift thermometry and single reference variable flip angle T₁...

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biomedical Engineering
• Medical Physics

Background:

• Accurate temperature monitoring is crucial for MR-guided focused ultrasound (MRgFUS) therapies.
• Existing thermometry methods have limitations in simultaneously assessing temperature changes in diverse tissue types, particularly fat.

Purpose of the Study:

• To evaluate the efficacy of a single reference variable flip angle sequence with multi-echo stack of stars acquisition (SR-VFA-SoS) for simultaneous thermometry.
• To assess the performance of both proton resonance frequency (PRF) shift and T1-based thermometry in an in vivo rabbit model during MRgFUS.

Main Methods:

• The SR-VFA-SoS sequence was employed at 3T in a rabbit model (n=7) during MRgFUS.
• Distinct tissue locations (muscle, fat, and their interface) were heated, and temperature changes were measured simultaneously using PRF shift and T1-based methods.
• The T1-temperature coefficient for fat was determined ex vivo and applied for in vivo temperature mapping.

Main Results:

• The SR-VFA-SoS sequence achieved a temporal resolution of 1.71 seconds at 1.5x1.5x2 mm voxel resolution.
• PRF shift thermometry was insensitive to heating in fat, while T1-based thermometry detected temperature changes in fat (mean coefficient: 1.9%/°C ± 0.2%/°C).
• Thermometry precision was 0.76°C ± 0.18°C for PRF shift in muscle and 1.93°C ± 0.60°C for T1-based thermometry in fat.

Conclusions:

• The SR-VFA-SoS sequence enables simultaneous MR thermometry using both PRF shift and T1-based methods.
• This technique provides effective temperature monitoring for both aqueous and fatty tissues during MRgFUS procedures in vivo.