## 6 General Recommendations
### Fat Suppression  
In radial imaging, the fat signal should be suppressed as much as possible in case fat information is not of interest, as it helps to minimize strong streaking artefacts and  
Figure 9: Panel (**A**) Water-only and fat-only images, and corresponding parametric maps of water fraction and fat fraction of a healthy adult subject as obtained using the proposed 6D free-running framework (x-y-z-cardiac-respiratory-echo) at 1.5 T. Panel (**B**) Cardiac fat fraction maps in a transversal view for each phase of the cardiac cycle during end-expiration as obtained using the proposed 6D free-running framework in a healthy adult subject at 1.5 T, allowing tracking of the displacement of pericardial fatty regions throughout the cardiac cycle. Figure created using the original source images by [PERSON] et al. [58] with author permission.  
image blurring caused by fat-water chemical shift. Fat suppression in MRI typically begins with a fat suppression preparation module that suppresses the MRI signal from fat tissue. As the fat signal recovers over time, multiple k-space lines can be collected. In Cartesian sampling, k-space sampling can be arranged so that the k-space centre is sampled when the fat signal is fully nulled following the fat suppression preparation. Although some k-space lines will always be sampled with a residual fat signal, these measurements can be deliberately acquired in the outer k-space regions, reducing their influence on image contrast. However, when using radial imaging, the performance of fat suppression can be compromised due to the repeated sampling of the k-space centre. Consequently, all k-space measurements, whether with or without fat signal, equally contribute to the final image. This prevents effective fat suppression in radial MRI and necessitates more advanced suppression strategies. Although water excitation techniques can be used, they are sensitive to magnetic field inhomogeneity at high fields, potentially causing unwanted signal loss. Recently, two fat suppression techniques for 3D radial imaging have been proposed, including lipid-insensitive binomial off-resonant radiofrequency excitation (LIBRE) [66] and fast interrupted steady-state (FISS) [67].  
In 2019, [PERSON] et al. implemented, optimized, and evaluated LIBRE [66], which uses two non-selective off-resonant rectangular radiofrequency sub-pulses, for fat suppression in the FRF [68]. Following parameter optimization using Bloch equations and in vitro validation, the optimized LIBRE pulses were evaluated for their use in the FRF in 20 adult subjects at 1.5 T. This LIBRE implementation was demonstrated to improve blood-fat contrast, vessel detection, and vessel sharpness when compared to other fat suppression methods, including water excitation and an interrupted free-running sequence using a chemically selective saturation (CHESS) fat saturation pulse. LIBRE thereby enabled superior fat suppression in the FRF without interrupting the 3D radial sequence, albeit with a penalty in scan time compared to its non-fat suppression counterpart.  
Another proposed fat suppression technique for 3D radial imaging is FISS, which has already shown its effectiveness in providing high SNR and blood-muscle contrast while simultaneously suppressing the fat signal under certain conditions when using bSFFP in 2D imaging [67]. In 2020, [PERSON] et al. developed and evaluated the use of FISS in 3D radial imaging to implement fat suppression in the FRF [69]. After optimization using numerical simulations and phantom experiments, they evaluated fat suppression in volunteers at both 1.5 and 3 T. These results demonstrated a significantly decreased fat signal using FISS compared to standard bSSFP at both field strengths (Figure 10). With only a modest increase in scan time, high-resolution fat-suppressed 5D whole-heart imaging using the FRF could be performed, and FISS is currently the method of choice for fat suppression in the FRF.