Simultaneous spin-echo refocusing

Abstract

A new approach to spin-echo imaging is presented in which the 180 degrees RF pulse refocuses two or more spin-echoes at different positions in the readout period. When simultaneous echo refocusing (SER) is implemented using multiple 180 degrees pulses, an undesirable mixing of stimulated echoes and primary echoes from different slices can occur. A novel periodic gradient spoiler scheme eliminates this potential source of artifacts without spoiling the correctly timed stimulated echoes, which, similar to RARE (TSE) sequences, add coherently to the primary echoes. Comparisons show equivalent artifact elimination using phase cycling, periodic spoiling, and a previously developed spoiling scheme for non-Carr-Purcell-Meiboom-Gill sequences. A comparison of head images at 1.5 T acquired with SER-TSE and conventional TSE T1-weighted sequences show no degradation in image quality nor SNR. T2-weighted imaging is not achievable with the current implementation, but possible solutions are proposed. The proposed technique might prove especially beneficial at higher field strengths, where the reduced number of refocusing pulses for multislice SER-TSE decreases RF power deposition. SER spin-echo imaging offers an approach that is very different from low flip angle imaging to mitigate RF heating limitations in high-field clinical imaging.