Temperature Dependence of the Susceptibility of Fat Leads to Significant Temperature Errors in PRFS-based MR Thermometry

Proton resonance frequency shift (PRFS)‐based MR thermometry is hampered by temporal field changes. Temporal changes in the susceptibility distribution lead to field changes and are therefore a possible source of errors. The susceptibility of fat, χfat, is temperature dependent, in the same order of magnitude as the temperature dependence of the chemical shift of water (0.01 ppm/° C). PRFS‐based temperature measurements may therefore be corrupted by non‐local field effects due to temperature induced susceptibility changes in fatty tissue. We performed simulations to quantify the influence of dχfat/dT on PRFS‐based MR temperature maps during thermal interventions in the breast. Susceptibility distributions were calculated for a 3D breast model without and with a stationary Gaussian temperature distribution and a maximum temperature of 57° C. Subsequently, the magnetic field was calculated in Fourier‐domain from these susceptibility distributions. Changes in the magnetic field distribution were quantified b...