Frequency-Selective Asymmetric Spin-Echo EPI with Parallel Imaging For Fast Internally Referenced MR Thermometry

Markus Nikola Streicher¹, Andreas Schfer¹, Dirk Mller¹, Carsten Kgler¹, Enrico Reimer¹, Bibek Dhital¹, Robert Trampel¹, Debra Rivera¹, Andr Pampel¹, Dimo Ivanov¹, Robert Turner¹

The proton resonance frequency shift MR thermometry method is inherently very sensitive to magnetic field perturbations in time. We simulated and tested a new referenced spin-echo (SE) EPI sequence which solves these problems reliably, efficiently and quickly. Frequency-selectivity of the SE sequence is achieved by using different slice-select gradient amplitudes for excitation and refocusing, making it easy to image water and a reference substance separately. The sequence alternately images each species, and thereby allows fast voxel-wise correction for magnetic field changes in a working range of 1ppm and excitation flip angles from 0 to 130.