Novel Parametric Mapping: T1 mapping and Diffuse Myocardial Fibrosis
New CMR techniques including T1 mapping for detection of diffuse myocardial fibrosis by quantifying extracellular matrix expansion have been developed to overcome the limitations of LGE132-134. T1 mapping is a parametric map of the myocardium that is generated from a series of image acquired at different times of T1 recovery curve after exposure to an inversion pulse135. The details of this technique is beyond the scope of this review. By assessing the differences between the pre-contrast and post-contrast T1 values in the myocardium and blood, the heart can be divided into the cellular and extracellular compartments. The relative distribution of gadolinium in the blood pool and the myocardium can then be used to estimate the extracellular volume (ECV) matrix136. It is known that native or pre-contrast T1 is prolonged in the setting of excess water content or edema in the tissue and is shortened when there is increase fibrosis. Studies have concluded that T1 mapping can detect diffuse myocardial fibrosis before evidence of LGE and can detect earlier disease (Fig 8a-l) 137, 138. In a small study, Soslow et al. demonstrated that DMD patients have elevated myocardial native T1 and ECV in the setting of normal LVEF and in the absence of LGE and concluded this may be useful in trials to detect occult cardiomyopathy before development of LGE139, 140. However, a larger multi-center double-blinded randomized aldosterone inhibition study between eplerenone and spironolactone showed attenuation of cardiac function by circumferential strain but no change in T1 or ECV between baseline and follow-up in either group131. This study however, enrolled older DMD patients with significant LGE already and the extent of DMD-CM may already be too advance. Future larger longitudinal studies in broader age range may help elucidated the utility of T1 mapping and ECV.