Development of a novel 10‐echo multi‐contrast sequence based on <scp>EPIK</scp> to deliver simultaneous quantification of <scp>T₂</scp> and <scp>T₂^*</scp> with application to oxygen extraction fraction

Abstract

Purpose The simultaneous quantification of T 2 and T 2 * maps based on fast sequences for combined GE and SE acquisition has rekindled research and clinical interest by offering a wide range of attractive applications, e.g., dynamic tracking of oxygen extraction fraction (OEF). However, previously published methods based on EPI‐readouts have been hindered by resolution and the number of acquired echoes. Methods This work presents a novel 10‐echo GE‐SE EPIK (EPI with keyhole) sequence for the rapid quantification of T 2 '. T 2 /T 2 * maps from the GE‐SE EPIK sequence were validated using three phantoms and 15 volunteers at 3T. The incorporation of a sliding window approach, combined with the full sampling of the k‐space center inherent to EPIK, enables a high effective temporal resolution. That is, for an eight‐slice breath‐hold experiment, a temporal sampling rate of eight reconstructed slices per 1.1 s. Results In comparison with repeated single‐echo SE, multi‐echo GE, and spectroscopy methods, the GE‐SE EPIK sequence shows good agreement in quantifying T 2 /T 2 * values, while the gray matter/white matter separation yielded the expected contrast differentiation. The OEF was calculated with a view to an initial application with clinical relevance, producing results comparable to those in the literature and with good sensitivity in breath‐hold experiments. Conclusions GE‐SE EPIK provides increased resolution and more echoes, including two SEs, than comparable sequences. Moreover, GE‐SE EPIK achieves this within an acquisition time of 57 s for 20 slices (matrix size = 128×128; FOV = 24 cm) and with a reasonably short TE for the final echo (114 ms). The sequence can dynamically track OEF changes in a breath‐hold experiment.

Topics & Concepts