title: Magnetic resonance elastography as a method to estimate myocardial contractility.
abstract: OBJECTIVE
  To determine whether increasing epinephrine infusion in an in vivo pig model is associated with an increase in end-systolic magnetic resonance elastography (MRE)-derived effective stiffness.
  
  
  METHODS
  Finite element modeling (FEM) was performed to determine the range of myocardial wall thicknesses that could be used for analysis. Then MRE was performed on five pigs to measure the end-systolic effective stiffness with epinephrine infusion. Epinephrine was continuously infused intravenously in each pig to increase the heart rate in increments of 20%. For each such increase end-systolic effective stiffness was measured using MRE. In each pig, Student's t-test was used to compare effective end-systolic stiffness at baseline and at initial infusion of epinephrine. Least-square linear regression was performed to determine the correlation between normalized end-systolic effective stiffness and increase in heart rate with epinephrine infusion.
  
  
  RESULTS
  FEM showed that phase gradient inversion could be performed on wall thickness ≈≥1.5 cm. In pigs, effective end-systolic stiffness significantly increased from baseline to the first infusion in all pigs (P = 0.047). A linear correlation was found between normalized effective end-systolic stiffness and percent increase in heart rate by epinephrine infusion with R(2) ranging from 0.86-0.99 in four pigs. In one of the pigs the R(2) value was 0.1. A linear correlation with R(2) = 0.58 was found between normalized effective end-systolic stiffness and percent increase in heart rate when pooling data points from all pigs.
  
  
  CONCLUSIONS
  Noninvasive MRE-derived end-systolic effective myocardial stiffness may be a surrogate for myocardial contractility.
authors.affiliation: Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA.
authors.forename: Arunark
authors.initials: A
authors.lastname: Kolipaka
authors.forename: Shivani R
authors.initials: SR
authors.lastname: Aggarwal
authors.forename: Kiaran P
authors.initials: KP
authors.lastname: McGee
authors.forename: Nandan
authors.initials: N
authors.lastname: Anavekar
authors.forename: Armando
authors.initials: A
authors.lastname: Manduca
authors.forename: Richard L
authors.initials: RL
authors.lastname: Ehman
authors.forename: Philip A
authors.initials: PA
authors.lastname: Araoz
mesh_terms: D000465:Algorithms; D000818:Animals; D003198:Computer Simulation; D055119:Elastic Modulus; D054459:Elasticity Imaging Techniques / Q000379:methods*; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008955:Models, Cardiovascular; D009200:Myocardial Contraction / Q000502:physiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013552:Swine; D016277:Ventricular Function, Left / Q000502:physiology*