Proton resonance frequency-based thermometry for aqueous and adipose tissues

Area of Science:

• Biomedical Engineering
• Medical Imaging
• Therapeutic Monitoring

Background:

• Proton resonance frequency (PRF)-based thermometry is a magnetic resonance (MR) imaging technique used for temperature mapping.
• Fatty tissues pose a challenge for PRF thermometry as fat is insensitive to heat, corrupting temperature-sensitive phase variations.
• Accurate temperature monitoring is crucial for various medical applications, including thermal therapies and disease diagnosis.

Purpose of the Study:

• To develop and validate a PRF-based thermometry method capable of reconstructing accurate temperature maps in tissues containing fat.
• To address the limitations of conventional PRF thermometry caused by the presence of fat's phase insensitivity.

Main Methods:

• A novel PRF-based method was proposed to eliminate fat's phase contribution by estimating and subtracting a temperature-insensitive fat vector.
• Complex MR image vectors representing voxel magnetization were analyzed; a circle fit to time-series vectors identified the fat vector.
• The method was validated using gel phantoms with varying fat content and ex vivo porcine tissues under water-bath and focused ultrasound (FUS) heating.

Main Results:

• The proposed method demonstrated good agreement with optical fiber temperature probes, with high R-squared values (0.994 in gels, 0.947 in ex vivo tissue).
• Bland-Altman analysis showed low bias (0.49°C in gels, -0.14°C in ex vivo tissue) and narrow confidence intervals (±1.60°C and ±3.26°C, respectively).
• A significant temperature discrepancy (up to 28%) was observed between the proposed and conventional PRF methods in fatty tissues during FUS heating, highlighting the proposed method's advantage.

Conclusions:

• The developed PRF-based thermometry method successfully reconstructs accurate temperature maps in the presence of fat.
• This technique offers improved accuracy for temperature measurements in clinically relevant tissues such as breast, abdomen, prostate, and bone marrow.
• The method holds promise for enhancing the efficacy and safety of thermal monitoring in various medical applications.