A k-space-based method to measure and correct for temporal B₀ field variations in MR temperature imaging

Area of Science:

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

Background:

• MR thermometry is crucial for monitoring tissue temperature during interventions.
• Temporal variations in the main magnetic field (B0) can introduce significant errors in MR thermometry.
• Existing methods may struggle to correct for dynamic B0 fluctuations, especially those induced by physiological motion like respiration.

Purpose of the Study:

• To present a novel method for dynamic MR temperature imaging using phase changes in repeated Cartesian k-space measurements.
• To monitor and correct for changes in the magnetic field (B0) during MR thermometry.
• To improve the accuracy and reliability of MR temperature measurements in the presence of B0 drift and motion.

Main Methods:

• Utilized phase variations from repeated Cartesian k-space measurements to detect B0 field changes.
• Applied the method to focused ultrasound heating experiments in gelatin phantoms and ex vivo pork samples.
• Simulated respiratory motion to test the robustness of the technique under dynamic conditions.

Main Results:

• Phase variations due to B0 drift and respiration were readily detected.
• Temperature measurement variability was significantly reduced: SD decreased from 0.81°C to 0.22°C (with breathing) in gelatin.
• Accuracy in non-heated regions improved, with RMS error decreasing from 4.73°C to 1.47°C (with breathing) in gelatin.
• Correction did not compromise temperature accuracy in heated regions.

Conclusions:

• Phase changes in Cartesian k-space acquisitions can directly measure B0 variations in MR thermometry.
• The presented correction technique effectively improves temperature accuracy and reduces variability.
• This method offers a robust solution for dynamic MR temperature imaging, particularly in the presence of physiological motion.