Temperature quantification using the proton frequency shift technique: In vitro and in vivo validation in an open 0.5...

Area of Science:

• Medical Imaging
• Biophysics
• Interventional Radiology

Background:

• Open magnetic resonance (MR) scanners offer advantages for tumor targeting and thermal monitoring during radiofrequency (RF) ablation.
• Accurate temperature quantification is crucial for effective and safe RF ablation procedures.

Purpose of the Study:

• To evaluate the feasibility of the proton frequency shift (PFS) technique for quantitative temperature monitoring during RF ablation in an open 0.5 T MR system.
• To synthesize thermal maps using PFS and assess temperature accuracy under ex vivo and in vivo conditions.

Main Methods:

• Proton frequency shift (PFS) technique employed for temperature quantification.
• Gradient echo (GRE) pulse sequences tested for thermal mapping.
• Experiments conducted on agarose gel, ex vivo paraspinal muscle, and in vivo porcine paraspinal muscle.
• Comparison with fiberoptic thermometer readings for calibration and validation.

Main Results:

• Calibration experiments yielded a chemical shift factor of 0.011 ± 0.001 ppm/°C in agarose gel.
• Temperature uncertainty decreased with lower bandwidths, reaching ±0.8°C at 2.5 kHz.
• In vitro paraspinal muscle experiments showed a chemical shift factor of 0.008 ± 0.001 ppm/°C and temperature uncertainty of ±2.7°C.
• In vivo porcine experiments resulted in a higher temperature uncertainty of ±4.3°C compared to in vitro conditions.

Conclusions:

• Quantitative temperature monitoring of RF ablation is feasible using the PFS technique in a 0.5 T open MR scanner.
• The PFS technique provides accurate thermal mapping for MR-guided RF ablation.
• Further optimization may be needed to reduce temperature uncertainty in in vivo applications.