## 5 Clinical Applications
### Anatomical Imaging and Coronary Angiography  
High-resolution imaging of the heart, its coronary arteries, and the great vessels plays an increasingly important role in the detection and assessment of cardiovascular diseases, such as coronary artery disease (CAD) and congenital heart diseases (CHDs) [40; 41; 42]. Although coronary angiography (CAG) using X-rays is the reference standard for assessing CAD, it is invasive, uses ionizing radiation, and poses a small risk of complications. Coronary magnetic resonance angiography (CMRA) is a potential alternative with several advantages, including its inherent soft-tissue contrast and lack of ionizing radiation [43].  
Over the past 25 years, CMRA has seen significant advancements but is still primarily used in research at specialized academic centres only. Its main drawbacks are the time-inefficient data collection and susceptibility to motion-induced artefacts. CMRA data collection is limited to the brief window of coronary quiescence (-50-150 ms), typically in mid-diastole, using electrocardiogram triggering. Achieving adequate high-resolution volumetric coverage therefore requires a large number of cardiac cycles, necessitating a free-breathing acquisition with advanced respiratory motion compensation. The SG concept, and ultimately the fully automated FRF, enabled complete cardiac and respiratory motion-resolved whole-heart imaging.  
Already in 2014, [PERSON] et al. evaluated coronary angiography and cardiac cine imaging capabilities using a simplified 4D version of the FRF (respiratory motion correction instead of resolving respiratory motion and without a CS reconstruction) [9]. When employed in nine healthy adult volunteers at 1.5 T with an isotropic spatial resolution of 1.15 mm\({}^{3}\), coronary artery image quality was very similar to that of a standard ECG-triggered reference acquisition and good agreement was found for cardiac volumes and ejection fractions between 4D and standard 2D cine imaging. Although the signal-to-noise ratio (SNR) was lower given the lower steady-state magnetization level and undersampling penalty, the 4D approach provided information about coronary anatomy at multiple time points in the cardiac cycle, along with data on ventricular function.  
In 2022, [PERSON] et al. investigated the role of the 5D cardiac and respiratory motion-resolved FRF for coronary angiography in paediatric CHD patients on a 1.5 T scanner [29]. All patients were administered ferumoxytol, an MRI contrast agent that circulates in the bloodstream for an extended period compared to standard gadolinium-based contrast agents [44]. Ferumoxytol therefore allows an extended image acquisition time which supports imaging with high spatial and temporal resolution which is particularly advantageous for paediatric patients with small anatomical structures and rapid heart rates [45]. Contrast-enhanced CMRA using the FRF was successfully employed and provided an excellent definition of cardiac anatomy--including that of the coronary arteries--in both intubated and free-breathing paediatric CHD patients (Figure 6). This clinical study underlined the simplicity, efficiency, and feasibility of contrast-enhanced CMRA using the FRF in paediatric CHD patients and further paved the way for its introduction into clinical workflows.