View Order With Arbitrary Center Echoes

To provide explicit, vendor-independent view-order constructions that enable selection of an arbitrary center echo in multi-shot imaging, with a focus on RARE and MPRAGE.

Vendor-independent view-order methods were developed to assign echo and shot indices to a prescribed set of phase encodes, enabling explicit selection of the center echo and avoiding large discontinuities near k-space center. The view-order methods were implemented in 2D RARE, 3D RARE, and MPRAGE, and evaluated in phantom and in vivo experiments, where the effects of the different methods were explored. An interactive dashboard was provided to reproduce them.

All methods enabled placing the chosen echo/shot index at the k-space center without changing other scan parameters. In RARE, varying the center echo produced the expected shift in $T_2$ weighting. In MPRAGE, varying $c$ produced the expected shift in $T_1$ weighting, in agreement with simulations. Artifact patterns in RARE were consistent with discontinuities and symmetry properties of the echo-index distribution.

Arbitrary-center view orders decouple scan parameters such as echo train length, matrix size, and undersampling factors, from center-echo selection. The presented constructions are compatible with common sampling strategies (e.g., partial Fourier, parallel imaging, and elliptical coverage) and sequences. Arbitrary center echoes allow for more control over image contrast and present an additional degree of freedom in sequence design.