Fast spectroscopic imaging for non-invasive thermometry using the Pr[MOE-DO3A] complex

The praseodymium complex of 10-(2-methoxyethyl)-1,4,7,10-tetraaza-cyclodode cane-1,4,7-triacetate) was evaluated as a temperature-sensitive contrast ag ent using the temperature dependence (similar to 0.12 ppm degrees C-1) of t he chemical shift of its methoxy side group signal. Pr[MOE-DO3A] was employ ed in combination with spectroscopic imaging (ST) methods for the determina tion of spatially resolved 2D and 3D temperature distributions in phantoms. Conventional SI and fast echo planar SI sequences (EPSI) were implemented on a 4.7 T MR imaging system fulfilling the demands for non-invasive thermo metry (NIT) with respect to thermal and temporal resolution, being <1 degre es C and <20 s total measuring time, respectively. The sequences are based on a fast spin echo SI method taking into account the very short relaxation times of the Pr complex methoxy group (T-1 = 28 ms, T-2 = 13 ms) and its c hemical shift difference (-24 ppm) from water. Calibration curves were meas ured in a uniformly heated water phantom and 2D SI methods were applied to dynamic heating experiments. The average differences between the temperatur es measured via fibreoptic thermometer and those derived from the spectrosc opic methods were less than or equal to 0.2 degrees C. Furthermore, 3D EPSI experiments with a 16 x 16 x 16 matrix size yielded temperature measuremen ts within 17 s from voxels of size 3 x 3 x 3 mm(3).