Rapid flow-artifact-free high-resolution T₂ mapping via multi-shot multiple overlapping-echo detachment imaging

The aim is to develop a T₂ mapping method with submillimeter spatial resolution, approximately 1-minute acquisition time, large volume coverage, and no extra burden on the console or coil setups. Additionally, to develop an associated approach correcting inter-shot phase variations caused by pulsatile CSF.

Multi-shot (msh-) acquisition scheme was integrated into multiple overlapping-echo detachment imaging (MOLED) to alleviate pitfalls of single-shot MOLED (e.g., excessive voxel size and B₀-induced geometric distortion) from the physical aspect. Discontinuous phase jumps were corrected via deep learning, leveraging the pattern incoherence between desired signal and undesired artifacts. Methodological feasibility was validated with phantoms (at 3 T and 7 T) and humans (at 3 T).

Referring to spin-echo (SE), phantom/human results exhibited a mean absolute error of 1.11/0.89 ms, and linear regression of phantom results revealed a slope of 0.994 (R² = 0.995). Referring to turbo SE, msh-MOLED demonstrated good coincidence of structural depiction. In data acquired with different scanners and scanning parameters, errors from CSF-induced inter-shot phase inconsistency were successfully eliminated without autocalibration kernel, navigators, gating equipment, nor time-consuming postprocessing.

A T₂ mapping method with submillimeter spatial resolution and high clinical practicality is proposed and validated. Inter-shot phase variation, a nuisance factor to sequences using segmented k-space acquisition, is addressed in a navigator-free and calibrationless manner, retaining the quantification accuracy and acquisition rapidness of msh-MOLED against pulsatile CSF. This work suggests that the trajectory-related ghost artifacts may be removed through specific spatial encoding and image inpainting.