## 3 The Fully Automated Cardiac Free-Running Framework
### Key Advantages  
As already briefly discussed, conventional cardiac MRI relies heavily on a reliable ECG signal for prospective or retrospective gating to 'freeze' cardiac motion, and on repetitive breath-holding or inefficient respiratory navigators to eliminate respiratory motion. If these requirements are not sufficiently met, the resulting images may become blurred and show motion artefacts, potentially making them unsuitable for clinical decision-making. Accurate R-wave detection in the ECG signal is regularly hindered by unwanted overlaid signals from the magnetohydrodynamic effect [25] and rapid gradient switching, in particular during continuous acquisitions such as cine imaging. Additionally, repetitive breath-holds can cause patient discomfort and fatigue, or may even be impossible for some patients. While diaphragmatic drift may occur during a breath-hold, consecutive breath-holds can also be inconsistent, leading to overlapping slices and functional measurement errors. Conversely, free-running cardiac MRI uses an SG sequence that extracts cardiac and respiratory motion signals directly from the acquired image data, eliminating the need for an ECG signal and repetitive breath-holds. This not only precludes ECG signal problems and improves patient comfort, but also speeds up and simplifies the preparation of patients before scanning.  
Figure 5: The obtained 5D image dataset can be visualised in various ways. (**A**) By fixing a specific respiratory motion state and looping through the cardiac phases, a cardiac 3D cine image is obtained (x-y-z-cardiac). (**B**) By fixing a specific cardiac phase and looping through the respiratory motion states, a respiratory 3D cine image is obtained (x-y-z-respiratory). (**C**) By fixing both a specific cardiac phase and respiratory motion state, a static 3D volume is obtained (x-y-z). For both dynamic 3D cines (**A**,**B**) and the static 3D volume (**C**), every desired (double) oblique cardiac view can be retrospectively selected using a multiplanar reconstruction.  
Additionally, standard 2D cardiac imaging requires the time-consuming and proficiency-demanding planning of (double) oblique cardiac views before acquisition, all while the patient remains in the scanner without data being collected. This leads to low acquisition efficiency. Furthermore, as each operator plans these cardiac views slightly differently, operator variability may be introduced, potentially affecting the resulting quantitative measurements. Finally, all desired cardiac views must be predetermined when using conventional 2D cardiac imaging, as no additional views can be created later. In contrast, free-running cardiac MRI addresses all these challenges. It eliminates the need for double oblique planning as only a 3D acquisition volume needs to be positioned around the heart based on the initial survey/localizer scan. Any desired cardiac view can be generated afterwards using an MPR of the 3D image (for each cardiac phase and respiratory state). This feature not only provides tremendous freedom in analysing the images but allows for additional measurements that are often not planned on beforehand, such as assessing atrial volumes and coronary arteries. Free-running MRI enables cardiac imaging to be performed by any operator, and not just by those specialized or specifically trained in CMR.  
Finally, when scanning paediatric patients, general anaesthesia and intubation are usually required to enable breath-holding [26]. This not only carries risks for paediatric patients but also requires the presence and supervision of a significant additional workforce of medical personnel [27; 28]. When using the FRF, however, breath-holding is no longer required which obviates this time-consuming, costly, and potentially dangerous procedure [29].