# Robust Autocalibrated Structured Low-Rank EPI Ghost Correction

## TL;DR

This paper introduces RAC-LORAKS, a robust structured low-rank method for EPI ghost correction that does not rely on perfect autocalibration data and improves ghost suppression across various imaging scenarios.

## Contribution

RAC-LORAKS extends previous autocalibrated low-rank methods by jointly considering autocalibration and EPI data, enhancing robustness to imperfect calibration and enabling multi-contrast reconstruction.

## Key findings

- Effective ghost suppression in complex EPI scenarios
- Robust to imperfect autocalibration data
- Outperforms state-of-the-art methods in simulations and in vivo tests

## Abstract

Purpose: We propose and evaluate a new structured low-rank method for EPI ghost correction called Robust Autocalibrated LORAKS (RAC-LORAKS). The method can be used to suppress EPI ghosts arising from the differences between different readout gradient polarities and/or the differences between different shots. It does not require conventional EPI navigator signals, and is robust to imperfect autocalibration data. Methods: Autocalibrated LORAKS is a previous structured low-rank method for EPI ghost correction that uses GRAPPA-type autocalibration data to enable high-quality ghost correction. This method works well when the autocalibration data is pristine, but performance degrades substantially when the autocalibration information is imperfect. RAC-LORAKS generalizes Autocalibrated LORAKS in two ways. First, it does not completely trust the information from autocalibration data, and instead considers the autocalibration and EPI data simultaneously when estimating low-rank matrix structure. And second, it uses complementary information from the autocalibration data to improve EPI reconstruction in a multi-contrast joint reconstruction framework. RAC-LORAKS is evaluated using simulations and in vivo data, including comparisons to state-of-the-art methods. Results: RAC-LORAKS is demonstrated to have good ghost elimination performance compared to state-of-the-art methods in several complicated EPI acquisition scenarios (including gradient-echo brain imaging, diffusion-encoded brain imaging, and cardiac imaging). Conclusion: RAC-LORAKS provides effective suppression of EPI ghosts and is robust to imperfect autocalibration data.