T1 mapping: characterisation of myocardial interstitial space

UNLABELLED: Myocardial fibrosis is always present in end-stage heart failure and is a major independent predictor of adverse cardiac outcome. Cardiac magnetic resonance (CMR) is an imaging method that permits a non-invasive assessment of the heart and has been established as the "gold standard" for the evaluation of cardiac anatomy and function, as well as for quantifying focal myocardial fibrosis in both ischaemic and non-ischaemic heart disease. However, cardiac pathologies characterised by diffuse myocardial fibrosis cannot be evaluated by late gadolinium enhancement (LGE) imaging, as there are no reference regions of normal myocardium. Recent improvements in CMR imaging techniques have enabled parametric mapping of relaxation properties (T1, T2 and T2*) clinically feasible within a single breath-hold. T1 mapping techniques performed both with and without contrast enable the quantification of diffuse myocardial fibrosis and myocardial infiltration. This article reviews current imaging techniques, emerging applications and the future potential and limitations of CMR for T1 mapping. TEACHING POINTS: • Myocardial fibrosis is a common endpoint in a variety of cardiac diseases. • Myocardial fibrosis results in myocardial stiffness, heart failure, arrhythmia and sudden death. • T1-mapping CMR techniques enable the quantification of diffuse myocardial fibrosis. • Native T1 reflects myocardial disease involving the myocyte and interstitium. • The use of gadolinium allows measurement of the extracellular volume fraction, reflecting interstitial space.