# Simultaneous Multi-Slice MRI using Cartesian and Radial FLASH and Regularized Nonlinear Inversion: SMS-NLINV

## TL;DR

This paper introduces a calibrationless parallel imaging method called SMS-NLINV for accelerated simultaneous multi-slice MRI, demonstrating improved reconstruction quality with Cartesian and radial FLASH sequences in phantom and in-vivo experiments.

## Contribution

The paper extends the NLINV algorithm to enable simultaneous multi-slice MRI reconstruction without calibration, applicable to Cartesian and radial sampling schemes.

## Key findings

- Validated against ESPIRiT in Cartesian experiments.
- Improved results with multi-slice over single-slice imaging.
- Sampling schemes with complementary samples outperform similar schemes.

## Abstract

Purpose: The development of a calibrationless parallel imaging method for accelerated simultaneous multi-slice (SMS) MRI based on Regularized Nonlinear Inversion (NLINV), evaluated using Cartesian and radial FLASH. Theory and Methods: NLINV is a parallel imaging method that jointly estimates image content and coil sensitivities using a Newton-type method with regularization. Here, NLINV is extended to SMS-NLINV for reconstruction and separation of all simultaneously acquired slices. The performance of the extended method is evaluated for different sampling schemes using phantom and in-vivo experiments based on Cartesian and radial SMS-FLASH sequences. Results: The basic algorithm was validated in Cartesian experiments by comparison with ESPIRiT. For Cartesian and radial sampling, improved results are demonstrated compared to single-slice experiments, and it is further shown that sampling schemes using complementary samples outperform schemes with the same samples in each partition. Conclusion: The extension of the NLINV algorithm for SMS data was implemented and successfully demonstrated in combination with a Cartesian and radial SMS-FLASH sequence.