[5] It is the reference standard for the assessment of cardiac structure and function,[6] and is valuable for diagnosis and surgical planning in complex congenital heart disease.
[7] Combined with vasodilator stress, it has a role in detecting and characterizing myocardial ischemia due to disease affecting the epicardial vessels and microvasculature.
[8] Magnetic resonance angiography may be performed with or without contrast medium and is used to assess congenital or acquired abnormalities of the coronary arteries and great vessels.
[9] Obstacles to its wider application include limited access to scanners, lack of technologists and skilled clinicians, relatively high costs, and competing diagnostic modalities.
[11] Gadolinium based contrast medium is frequently used in CMR and has been associated with nephrogenic systemic fibrosis, predominantly using linear compounds in patients with renal disease.
[12] Genotoxic effects of cardiac MRI have been reported in vivo and in vitro,[13][14][15][16] but these findings have not been replicated by more recent studies,[17] and are unlikely to produce the complex DNA damage associated with ionizing radiation.
[19] Cine sequences of the heart are acquired using balanced steady state free precession (bSSFP) which has good temporal resolution and intrinsic image contrast.
[21] A study begins with localisers to assist with image planning, and then a set of retrospectively-gated cine sequences to assess biventricular function in standard orientations.
The left ventricular short axis cines are acquired from base to apex and are used for quantifying end-diastolic and end-systolic volumes, as well as myocardial mass.
Cost and availability mean that its use is often confined to patients with intermediate pre-test probability,[24] but it has been shown to reduce unnecessary angiography compared with guidelines-directed care.
[25] Conventional phase contrast imaging can be extended by applying flow-sensitive gradients in 3 orthogonal planes within a 3D volume throughout the cardiac cycle.
Examples of conditions in which CMR is often used include tetralogy of Fallot, transposition of the great arteries, coarctation of the aorta, single ventricle heart disease, abnormalities of the pulmonary veins, atrial septal defect, connective tissue diseases such as Marfan syndrome, vascular rings, abnormal origins of the coronary arteries, and cardiac tumors.
Some centers allow children to listen to music or watch movies through a specialized MRI-compatible audiovisual system to reduce anxiety and improve cooperation.
However, the presence of a calm, encouraging, supportive parent generally produces better results in terms of pediatric cooperation than any distraction or entertainment strategy short of sedation.
[27] Imaging at 3T field strength offers greater signal to noise ratio which can be traded for improved temporal or spatial resolution – which is of greatest utility in first-pass perfusion studies.
The phenomenon of nuclear magnetic resonance (NMR) was first described in molecular beams (1938) and bulk matter (1946), work later acknowledged by the award of a joint Nobel Prize in 1952.
In recent years, with the development of artificial intelligence techniques, the reporting and analysis of cardiac MRI are expected to be more efficient, facilitated by automatic deep learning tools.