Noninvasive temperature mapping with MRI using chemical shift water-fat separation.

Area of Science:

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

Background:

• Standard MRI thermometry methods are confounded by lipid signals in tissues like breast.
• Lipid protons lack temperature-induced frequency shifts, complicating accurate temperature mapping.
• Water-fat separation techniques are needed to isolate and utilize water proton signals for thermometry.

Purpose of the Study:

• To develop and validate a novel MRI method for accurate temperature mapping in water-lipid mixtures.
• To address the limitations of standard MRI thermometry in complex biological tissues.
• To demonstrate the capability of separating water and fat signals for improved temperature resolution and correction of artifacts.

Main Methods:

• Utilized generalized Dixon chemical shift-based water-fat separation to create distinct water and fat images.
• Employed a water and fat thermal MRI acquisition and postprocessing technique.
• Applied noninvasive heating to phantoms with varying water-to-fat ratios (30:70, 50:50, 70:30) using a phased radiofrequency array.
• Correlated MRI-derived temperatures with fiber optic temperature probe measurements.

Main Results:

• The water and fat thermal MRI method successfully mapped temperature changes in phantoms.
• Phase changes in the water signal accurately reflected temperature variations.
• Phase changes in the lipid signal effectively corrected for non-temperature-dependent phase shifts, including static magnetic field drift.
• Region of interest temperature values showed excellent agreement with fiber optic probes (-0.09 +/- 0.34 °C).

Conclusions:

• The developed water and fat thermal MRI method provides accurate and reliable temperature mapping in the presence of lipids.
• This technique overcomes limitations of conventional MRI thermometry in complex tissues.
• The method's ability to correct for magnetic field drift enhances its robustness for clinical applications.