sigpy implementation for rrsg challenge (ISMRM 2019) Original paper: Klaas P. Pruessmann, Markus Weiger, Peter Börnert, Peter Boesiger. Advances in sensitivity encoding with arbitrary k-space trajectories. Magn Reson Med. 2001 Oct;46(4):638-51.

Implement the flowchart

## Reconstruction for subsampled brain images

## Reconstruction results under different iteration number

## Reconstruction for cardiac undersampled images