Abstract 14535: Regional in vivo Assessment of Myocardial Stiffness Using 3d Magnetic Resonance Elastography in a Pig Model With Induced Myocardial Infarction

Introduction: Myocardial stiffness is a novel biomarker with both diagnostic and prognostic potential in a range of cardiac diseases. The application of a noninvasive imaging technique called Magnetic Resonance Elastography (MRE) to the heart enables the measurement of myocardial stiffness in vivo. The potential of this technique to assess regional myocardial stiffness has not yet been demonstrated. Hypothesis: MRE can regionally differentiate between normal and infarcted myocardial tissue. Methods: A myocardial infarction was induced in 5 pigs by embolizing the left circumflex artery with ceramic microspheres. Fourteen days post-surgery, imaging was performed in diastole on a 1.5 Tesla scanner (GE Healthcare, Waukesha, WI) with 3-mm isotropic resolution using an ECG-gated spin-echo echo-planar-imaging MRE sequence with 140 Hz vibrations. After MRE, the pig was sacrificed using potassium chloride solution and the heart was excised and cut into short-axis slices and stained with 2,3,5-triphenyltetrazolium chloride (TTC) to identify the location of the myocardial infarction. Uniaxial tensile testing was performed (MTS, Eden Prairie, MN) on sections of infarcted and remote myocardium. For each pig, MRE stiffness images were calculated, and the mean stiffness was reported over two manually drawn ROIs, prescribed off the magnitude image, over both the infarct and remote normal myocardium. Results & Conclusions: Increased stiffness in myocardial infarctions was observed (Figure 1) in all 5 pigs, with mean infarct stiffness = 4.6 kPa ± 0.7 and normal stiffness = 3.0 kPa ± 0.6 (p = 0.02). Ex vivo uniaxial mechanical testing showed the mean tensile modulus was 0.65 ± 0.08 MPa and 0.11 ±0.02 MPa (p= 0.012) for the infarct and normal myocardium, respectively. This marks the first time that regional myocardial stiffness has been directly measureable in vivo and the first time that cardiac MRE has been validated against a material-testing reference standard.