On Retrospective k-space Subsampling schemes For Deep MRI Reconstruction

TL;DR

This study evaluates how different k-space subsampling schemes affect deep learning MRI reconstruction quality, showing non-rectilinear schemes improve results, especially at high accelerations, and that training on such schemes enhances performance across various sampling methods.

Contribution

It investigates the impact of various k-space subsampling schemes on deep learning MRI reconstruction, highlighting the advantages of non-rectilinear sampling and multi-scheme training for improved image quality.

Findings

Non-rectilinear subsampling yields superior reconstruction performance.

Training on multiple schemes improves results across all sampling types.

Deep learning models trained on non-rectilinear data perform better at high accelerations.

Abstract

Acquiring fully-sampled MRI $k$-space data is time-consuming, and collecting accelerated data can reduce the acquisition time. Employing 2D Cartesian-rectilinear subsampling schemes is a conventional approach for accelerated acquisitions; however, this often results in imprecise reconstructions, even with the use of Deep Learning (DL), especially at high acceleration factors. Non-rectilinear or non-Cartesian trajectories can be implemented in MRI scanners as alternative subsampling options. This work investigates the impact of the $k$-space subsampling scheme on the quality of reconstructed accelerated MRI measurements produced by trained DL models. The Recurrent Variational Network (RecurrentVarNet) was used as the DL-based MRI-reconstruction architecture. Cartesian, fully-sampled multi-coil $k$-space measurements from three datasets were retrospectively subsampled with different accelerations using eight distinct subsampling schemes: four Cartesian-rectilinear, two Cartesian non-rectilinear, and two non-Cartesian. Experiments were conducted in two frameworks: scheme-specific, where a distinct model was trained and evaluated for each dataset-subsampling scheme pair, and multi-scheme, where for each dataset a single model was trained on data randomly subsampled by any of the eight schemes and evaluated on data subsampled by all schemes. In both frameworks, RecurrentVarNets trained and evaluated on non-rectilinearly subsampled data demonstrated superior performance, particularly for high accelerations. In the multi-scheme setting, reconstruction performance on rectilinearly subsampled data improved when compared to the scheme-specific experiments. Our findings demonstrate the potential for using DL-based methods, trained on non-rectilinearly subsampled measurements, to optimize scan time and image quality.