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.