Varying Gd-DTPA concentrations in phantoms. (A) MRI phase images before and after Gd-DTPA injection. No heating was applied. The red scale bar indicates the voxel locations in plots B and C. (B) Phase plot in which each line indicates the phase over time of a point in the phase image. The green bar indicates the time span during which Gd-DTPA was injected and mixed. The phase signal was not corrected for main magnetic field drifts. (C) Plot of the calculated temperature error over time. The apparent temperature change was corrected for magnet field drifts and was calculated from the magnetic field changes via the -0.01 ppm/°C relation [4, 8].