Phase‐encoded xSPEN: A novel high‐resolution volumetric alternative to RARE MRI.

Purpose: To develop a rapid, non‐CPMG high‐resolution volumetric imaging approach, exhibiting a speed and in‐plane resilience to field inhomogeneities comparable to RARE/turbo‐spin‐echo (TSE) while endowed with unique downsampling characteristics. Methods: A multi‐scan extension of cross‐term spatiotemporal encoding (xSPEN) is introduced and analyzed. The method simultaneously yields k_y/k_z data containing low and high frequency components, as well as transposed, low‐resolution z/y images. This dual k‐/spatial‐domain information is captured by a multi‐scan procedure that phase‐encodes k_y while simultaneously slice‐selecting z. A reconstruction scheme converting this information into high resolution 3D images with fully multiplexed volumetric coverage is introduced and exemplified. Results: Phase‐encoded xSPEN was tested by human brain imaging at sub‐mm resolutions. The method exceeded 2D TSE's sensitivity by factors of ≈3–4, while providing similar resolution and SNR as 3D TSE in ≈50% acquisition times. The method's contrast is dominated by T₂ and is free from “bright‐fat” effects associated to spin‐echo trains. Further acceleration is enabled by the method's downsampling abilities. Tradeoffs between encoding time, number of measurements, spatial resolution, SNR, and artifact levels are also laid out. Conclusion: A new MRI strategy is introduced delivering high in‐ and through‐plane resolutions while enjoying full Fourier multiplexing, leading to fast acquisitions with high SNR. [ABSTRACT FROM AUTHOR]