Correction of B0 Drift Effects in Magnetic Resonance Thermometry using Magnetic Field Monitoring Technique

Abstract

When magnetic resonance (MR) thermometry is performed for temperature monitoring during time-consuming thermal therapy like hyperthermia, tiny main magnetic field (B₀) drifts may cause significant errors in temperature readings inside the human subject. We propose a correction method of B₀ drift effects in MR thermometry, which is based on temperature-dependent proton resonance frequency shift (PRFS) of water molecules. We placed magnetic field monitoring (MFM) probes around the subject and we read the center frequency of MFM signals. By interpolating the center frequencies of MFM signals on the imaging slice, we computed phase correction maps for MR thermometry. We intermittently acquired MFM signals with performing MR thermometry at 3 Tesla during radiofrequency (RF) heating of a tissue-mimicking phantom. With the B₀ drift effect correction, the temperature readings of MR thermometry maps became similar to the temperature readings of an optic fiber temperature sensor embedded at the center of the phantom. We believe the proposed correction method can be used for MRI-guided thermal therapy in which precise temperature monitoring is critical.