Chemically Selective Asymmetric Spin-Echo EPI Phase Imaging for Internally Referenced MR Thermometry

Markus Nikola Streicher¹, Andreas Schfer¹, Bibek Dhital¹, Dirk Mller¹, Robin Martin Heidemann¹, Andre Pampel¹, Dimo Ivanov¹, Robert Turner¹

We implemented a novel spin-echo EPI sequence that can acquire phase images of different chemically-shifted protons at the same slice positions. Chemical selection was achieved by applying different slice-select gradient amplitudes for excitation and refocusing RF pulses, and phase sensitivity was obtained using an asymmetric EPI readout. MR Thermometry was then performed on a mixture of water and dimethyl sulfoxide (DMSO), which has a proton chemical shift of -2 ppm from water. The two compounds were then imaged alternately, water for temperature sensitivity and DMSO to monitor field changes. Fat can also be selectively imaged as a reference compound.