Abstract 16566: T1 Mapping Calculated from Look-Locker Sequences Reliably Assesses Interstitial Myocardial Fibrosis Compared with Histology, and Diastolic Dysfunction

Abstract

Introduction: Myocardial fibrosis plays a key role in systolic and diastolic cardiac failure. Recently, T1 mapping using optimized sequences has been demonstrated to correlate with the amount of diffuse myocardial fibrosis. However, T1 mapping techniques involve the use of special sequences which are solely found in research facilities. We intended to validate myocardial T1 mapping with the commonly available Look-Locker (LL) sequence and correlate it with histological fibrosis and LV systolic and diastolic function in an experimental model.

Methods: Acute MI was induced in 13 Yorkshire pigs by balloon occlusion of the proximal LAD for 60 minutes. Magnetic resonance imaging (MRI) at 3.0 Tesla and 3D-echocardiography were performed at 1 month post MI. T1 mapping was obtained from LL sequences 15 minutes after Gadolinium injection (0.2 mmol/kg). Diastolic function was assessed by MRI-derived time-volume curves and echocardiography. Animals were sacrificed and interstitial fibrosis in noninfarcted remote myocardium was measured by Masson trichrome staining.

Results: Postcontrast LL-T1 time of noninfarcted segments significantly correlated with amount of interstitial fibrosis assessed by histology in the same areas (r=-0.64, p=.04), but not with cardiomyocyte hypertrophy. There was a strong correlation between T1 time and 3D-longitudinal strain (r=-0.76, p<.01), but not with ejection fraction, 3D-circumferential strain or 3D-radial strain. Further, LL-T1 time correlated with MRI-derived diastolic function: first filling volume (r=0.66, p=.02) and first/second filling volume ratio (r=0.68, p=.02). LL-T1 time also correlated with echocardiography-derived diastolic function: E (r=0.60, p=.03) and isovolumic relaxation time (r=-0.66, p=.01). Finally, there was a trend in the correlation between T1 time with LV stiffness (r=-0.58, p=.06), E/E ratio (r=-0.52, p=.07) and color M-mode propagation velocity (r=0.5, p=.08).

Conclusions: Postcontrast T1 mapping calculated with a conventionally used LL sequence reliably assesses myocardial interstitial fibrosis. A shorter LL- T1 time was associated with increased diffuse fibrosis, reduced longitudinal strain, and worse diastolic function.