6 research outputs found
AliasNet: Alias Artefact Suppression Network for Accelerated Phase-Encode MRI
Sparse reconstruction is an important aspect of MRI, helping to reduce
acquisition time and improve spatial-temporal resolution. Popular methods are
based mostly on compressed sensing (CS), which relies on the random sampling of
k-space to produce incoherent (noise-like) artefacts. Due to hardware
constraints, 1D Cartesian phase-encode under-sampling schemes are popular for
2D CS-MRI. However, 1D under-sampling limits 2D incoherence between
measurements, yielding structured aliasing artefacts (ghosts) that may be
difficult to remove assuming a 2D sparsity model. Reconstruction algorithms
typically deploy direction-insensitive 2D regularisation for these
direction-associated artefacts. Recognising that phase-encode artefacts can be
separated into contiguous 1D signals, we develop two decoupling techniques that
enable explicit 1D regularisation and leverage the excellent 1D incoherence
characteristics. We also derive a combined 1D + 2D reconstruction technique
that takes advantage of spatial relationships within the image. Experiments
conducted on retrospectively under-sampled brain and knee data demonstrate that
combination of the proposed 1D AliasNet modules with existing 2D deep learned
(DL) recovery techniques leads to an improvement in image quality. We also find
AliasNet enables a superior scaling of performance compared to increasing the
size of the original 2D network layers. AliasNet therefore improves the
regularisation of aliasing artefacts arising from phase-encode under-sampling,
by tailoring the network architecture to account for their expected appearance.
The proposed 1D + 2D approach is compatible with any existing 2D DL recovery
technique deployed for this application
Aliasing Artefact Suppression in Compressed Sensing MRI for Random Phase-Encode Undersampling
Goal: Random phase-encode undersampling of Cartesian k-space trajectories is widely implemented in compressed sensing (CS) MRI. However, its one-dimensional (1-D) randomness inherently introduces large coherent aliasing artefacts along the undersampled direction in the reconstruction and, thus, degrades the image quality. This paper proposes a novel reconstruction scheme to reduce the 1-D undersampling-induced aliasing artefacts. Methods: The proposed reconstruction progress is separated into two steps in our new algorithm. In step one, we transfer the original two-dimensional (2-D) image reconstruction into a parallel 1-D signal reconstruction procedure, which takes advantage of the superior incoherence property in the phase direction. In step two, using the new k-space data obtained from the 1-D reconstructions, we implement a follow-up 2-D CS reconstruction to produce a better solution, which exploits the inherent correlations between the adjacent lines of 1-D reconstructed signals. Results: We evaluated the performance on various cases of typical MR images, including cardiac cine, brain, foot, and angiogram at the reduction factor up to 10 and compared the results with the conventional CS method. Experiments using the proposed method demonstrated faithful reconstruction of the MR images. Conclusion: Compared with conventional method, the new method achieves more accurate reconstruction results with 2-5 dB gain in peak SNR and higher structural similarity index. Significance: The proposed method improves image quality of the reconstructions and suppresses the coherent artefacts introduced by the random phase-encode undersampling