Echo planar time‐resolved imaging (EPTI)
Purpose To develop an efficient distortion‐ and blurring‐free multi‐shot EPI technique for time‐resolved multiple‐contrast and/or quantitative imaging. Methods EPI is a commonly used sequence but suffers from geometric distortions and blurring. Here, we introduce a new multi‐shot EPI technique termed echo planar time‐resolved imaging (EPTI), which has the ability to rapidly acquire distortion‐ and blurring‐free multi‐contrast data set. The EPTI approach performs encoding in k y ‐ t space and uses a new highly accelerated spatio–temporal CAIPI sampling trajectory to take advantage of signal correlation along these dimensions. Through this acquisition and a B 0 ‐informed parallel imaging reconstruction, hundreds of “time‐resolved” distortion‐ and blurring‐free images at different TEs across the EPI readout window can be created at sub‐millisecond temporal increments using a small number of EPTI shots. Moreover, a method for self‐estimation and correction of shot‐to‐shot B 0 variations was developed. Simultaneous multi‐slice acquisition was also incorporated to further improve the acquisition efficiency. Results We evaluated EPTI under varying simulated acceleration factors, B 0 ‐inhomogeneity, and shot‐to‐shot B 0 variations to demonstrate its ability to provide distortion‐ and blurring‐free images at multiple TEs. Two variants of EPTI were demonstrated in vivo at 3T: (1) a combined gradient‐ and spin‐echo EPTI for quantitative mapping of T 2 , T 2 * , proton density, and susceptibility at 1.1 × 1.1 × 3 mm 3 whole‐brain in 28 s (0.8 s/slice), and (2) a gradient‐echo EPTI, for multi‐echo and quantitative T 2 * fMRI at 2 × 2 × 3 mm 3 whole‐brain at a 3.3 s temporal resolution. Conclusion EPTI is a new approach for multi‐contrast and/or quantitative imaging that can provide fast acquisition of distortion‐ and blurring‐free images at multiple TEs.