A multi-inversion multi-echo spin and gradient echo echo planar imaging sequence with low image distortion for rapid quantitative parameter mapping and synthetic image contrasts

Purpose: Brain imaging exams typically take 10-20 min and involve multiple sequential acquisitions. A low-distortion whole-brain echo planar imaging (EPI)-based approach was developed to efficiently encode multiple contrasts in one acquisition, allowing for calculation of quantitative parameter maps and synthetic contrast-weighted images.

Methods: inversion prepared spin- and gradient-echo EPI was developed with sliceorder shuffling across measurements for efficient acquisition with T-1, T-2, and T-2* weighting. A dictionary-matching approach was used to fit the images to quantitative parameter maps, which in turn were used to create synthetic weighted images with typical clinical contrasts. Dynamic slice-optimized multi-coil shimming with a B-0 shim array was used to reduce B-0 inhomogeneity and, therefore, image distortion by >50%. Multi-shot EPI was also implemented to minimize distortion and blurring while enabling high in-plane resolution. A low-rank reconstruction approach was used to mitigate errors from shot-to-shot phase variation.

Results: The slice-optimized shimming approach was combined with in-plane parallel-imaging acceleration of 4x to enable single-shot EPI with more than eightfold distortion reduction. The proposed sequence efficiently obtained 40 contrasts across the whole-brain in just over 1 min at 1.2 x 1.2 x 3 mm resolution. The multishot variant of the sequence achieved higher in-plane resolution of 1 x 1 x 4 mm with good image quality in 4 min. Derived quantitative maps showed comparable values to conventional mapping methods.

Conclusion: The approach allows fast whole-brain imaging with quantitative parameter maps and synthetic weighted contrasts. The slice-optimized multi-coil shimming and multi-shot reconstruction approaches result in minimal EPI distortion, giving the sequence the potential to be used in rapid screening applications.