# Comparison between fast-interrupted steady-state (FISS) and rapid water-excitation pulses for fat signal suppression in free-running whole-heart MRI at 1.5 T

## TL;DR

This study compares different fat suppression techniques in heart MRI to reduce artifacts and improve image quality without using contrast agents.

## Contribution

The study evaluates and compares novel fat suppression methods (LIBOR, LIBRE, BORR) against FISS in free-running whole-heart MRI at 1.5 T.

## Key findings

- LIBOR achieved the highest contrast-to-noise ratio (CNRWater-Fat) in phantom experiments.
- FISS showed the highest blood-myocardium contrast in volunteers but differences were not statistically significant.
- LIBOR required significantly lower SAR compared to FISS, making it more energy-efficient.

## Abstract

Free-running whole-heart MRI using balanced steady-state free precession (bSSFP) sequences offer high SNR and myocardial tissue contrast. However, an inadequate fat signal suppression may introduce artifacts and is particularly challenging with non-Cartesian readouts. The aim of this study was to evaluate different fat-signal suppression methods for whole-heart free-running MRI at 1.5 T using numerical simulations, phantom, and cardiac MRI experiments without the use of contrast agents.

Binomial off-resonant rectangular (BORR), lipid insensitive binomial off-resonant RF excitation (LIBRE), and lipid insensitive binomial off-resonant (LIBOR) pulses were implemented within a 3D radial bSSFP sequence. Their pulse parameters were optimized for fat signal suppression at 1.5 T using simulations and phantom experiments. Optimized protocols, along with a free-running fast interrupted steady-state (FISS) and non-fat suppressed bSSFP sequence, were used to acquire phantom and cardiac data in five volunteers. SAR values were recorded. The SNR and CNRWater-Fat were measured in phantom data, while SNR and CNRBlood-Myocardium were quantified in volunteers using reconstruction without motion correction. Motion-resolved reconstructions were used for qualitative assessments. Statistical differences were analyzed using one-way ANOVA.

LIBOR had the highest CNRWater-Fat (276.8 ± 2.5) in phantoms, followed by LIBRE (268.1 ± 2.6), BORR (249.9 ± 2.2), and FISS (212.7 ± 2.7), though these differences were not statistically significant (p > 0.05). In volunteers, BORR had the highest SNR in the ventricular blood pool (17.0 ± 1.5), and LIBRE had the highest CNRBlood-Fat (29.4 ± 9.3). FISS had the highest CNRBlood-Myocardium (29.0 ± 8.9), but the differences were not significant (p > 0.05). Motion-resolved cardiac imaging showed comparable quality across all fat-suppressed sequences, with no significant streaking artifacts observed. Free-running bSSFP with LIBOR required the lowest SAR, up to a sixfold decrease compared with FISS.

The tested sequences performed similarly in SNR and CNR but LIBOR offered the lowest SAR, making it a promising candidate for applications where RF energy deposition is a concern.