Abstract 14687: Endogenous Molecular-Magnetic Resonance Imaging of Cardiac Fibrosis After Myocardial Infarction
Intro: MRI of cardiac fibrosis with gadolinium is indirect due to retention of contrast media in badly damaged tissue. Radio-frequency excitation of collagen leads to endogenous contrast via magnetization transfer (MT) with surrounding bulk water. We developed a MT-encoded cardiac sequence to characterize fibrosis after myocardial infarction (MI) in mice.
Methods: A retrospectively gated cine sequence encoded collagen-MT into the steady state longitudinal magnetization. An encoding module (28 gauss pulses, BW = 200Hz, 270°, time = 540ms) was inserted (Fig A) prior to a readout module (10°, TR=10.2ms, 100 repetitions, 128 repetitions of both modules). Images were acquired with saturation offsets incremented from -12 to +12 ppm, 1mm thickness, 0.1 x 0.1 mm resolution, and FOV of 2.56 x 2.56 cm on a 9.4T Bruker Biospec. MI was induced via coronary ligation in 8-10 week old male C57B6 mice (n = 7). Cine and MT-encoded MRI followed by delayed contrast enhancement (DCE) with Gd-DTPA occurred at 1, 7, 10, 14, and 21 days after MI. Infarct, border, and remote zones were defined by DCE patterns. Normalized Z-spectra from infarct and border zones were modeled as the convolution of remote zone spectra with a distribution function I(f) = A*γ2/(f2+ γ2). Regional fibrotic scores (F.S.) were calculated as FS = (A-1-1)*100. Hearts were excised and stained for collagen at 22 days post-MI.
Results: Divergence of regional Z-spectra started 7 days after MI (Fig B). Fibrotic score increased at day 7 and remained elevated in infarct zone myocardium (Fig C), reflecting rapid scar formation. In border zone myocardium, F.S. transiently increased at 7 days after MI, reflecting spatial redefinition of the border zone following infarct extension. Tissue staining revealed dense infarct zone collagen deposits, and mixed border zone deposits.
Conclusion: MT-encoded MRI enables quantitative in vivo measurement of fibrosis and can elucidate cardiac fibrotic processes without limitations of contrast agents.
- © 2013 by American Heart Association, Inc.