Dynamic T mapping by multi-spin-echo spatiotemporal encoding.

PURPOSE: To develop a pulse sequence for acquiring robust, quantitative T relaxation maps in real time.

METHODS: The pulse scheme relies on fully refocused spatiotemporally encoded multi-spin-echo trains, which provide images that are significantly less distorted than spin-echo echo planar imaging-based counterparts. This enables single-shot T mapping in inhomogeneity-prone regions. Another advantage of these schemes stems from their ability to interleave multiple scans in a reference-free manner, providing an option to increase sensitivity and spatial resolution with minimal motional artifacts.

RESULTS: The method was implemented in preclinical and clinical scanners, where single-shot acquisitions delivered reliable T maps in ≤200 ms with ≈250 µm and ≈3 mm resolutions, respectively. Ca. 4 times higher spatial resolutions were achieved for the motion-compensated interleaved versions of these acquisitions, delivering T maps in ca. 10 s per slice. These maps were nearly indistinguishable from multi-scan relaxometric maps requiring orders-of-magnitude longer acquisitions; this was confirmed by mice head and real-time mice abdomen 7T scans performed following contrast-agent injections, as well as by 3T human brain and breast scans.

CONCLUSION: This study introduced and demonstrated a new approach for acquiring rapid and quantitative T data, which is particularly reliable when operating at high fields and/or targeting heterogeneous organs or regions.