Cardiovascular MRI at 3 T & Beyond

In recent years the high and ultra-high magnetic field MRI scanners have started to leave the confinement of specialized and research oriented laboratories and progressively are entering the clinical use. There are several reasons to justify the progressive increase of the field such as better quality of images that is better spatial resolution, better signal to noise and contrast to noise ratio, or better temporal resolution, etc. However, while for some organs such as the brain the use of higher static field has un-doubtfully induced a substantial improvement in diagnostic performance for other body districts such as the cardiovascular one there is still a debate on the cost-benefit of transferring patients to the fields higher than 1.5T that is 3.0 and/or 7.0T. While, on one hand, pilot studies performed in highly qualified Centers show that there would be a significant benefit from the use of 3.0T mainly in some applications such as Myocardial Perfusion, Late Gadolinium Enhancement images and T1 mapping, on the other hand a systematic use of 3.0T has been considered unrealistic. This is because the overall quality of cardiac images is strongly affected by the presence of artefacts. Black blood images are much more prone to susceptibility artefacts while cine images show quite frequently the presence of flow related artefacts. Furthermore, in applications such as cine images, the advantages are more theoretical than real as the SAR limitation. A self block of the amount of energy transferred to the patient is unavoidably applied by the scanners, and this reduces the possible advantages related to the fast acquisition of images. However, technological development is progressively reducing the incidence of artefacts at 3.0T. The introduction of advanced cardiac shimming procedures to compensate the field in-homogeneities (ex. GRE based fieldmap acquisition followed by the optimization volume (see Figure 1), etc) might significantly improve the quality. Similarly an effort on optimization of acquisition parameters in the single patient, a more accurate detection of ECG signal, the use of more sophisticated receiving coils, innovative approaches to fill the k-space, etc might produce either black blood or white blood images which are competitive with the ones obtained at lower field. As a result of this broad technological advancement it is not surprising any more that Centers scanning daily an high number of cardiac patients might routinely adopt a 3.0T scanner (even if some limitations have to be still considered. For example, in patients undergoing T2* mapping the susceptibility artefacts can reduce the capability of quantitative approach in detecting relaxivity on a regional basis.