title: Submillimeter diffusion tensor imaging and late gadolinium enhancement cardiovascular magnetic resonance of chronic myocardial infarction.
abstract: BACKGROUND
  Knowledge of the three-dimensional (3D) infarct structure and fiber orientation remodeling is essential for complete understanding of infarct pathophysiology and post-infarction electromechanical functioning of the heart. Accurate imaging of infarct microstructure necessitates imaging techniques that produce high image spatial resolution and high signal-to-noise ratio (SNR). The aim of this study is to provide detailed reconstruction of 3D chronic infarcts in order to characterize the infarct microstructural remodeling in porcine and human hearts.
  
  
  METHODS
  We employed a customized diffusion tensor imaging (DTI) technique in conjunction with late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) on a 3T clinical scanner to image, at submillimeter resolution, myofiber orientation and scar structure in eight chronically infarcted porcine hearts ex vivo. Systematic quantification of local microstructure was performed and the chronic infarct remodeling was characterized at different levels of wall thickness and scar transmurality. Further, a human heart with myocardial infarction was imaged using the same DTI sequence.
  
  
  RESULTS
  The SNR of non-diffusion-weighted images was >100 in the infarcted and control hearts. Mean diffusivity and fractional anisotropy (FA) demonstrated a 43% increase, and a 35% decrease respectively, inside the scar tissue. Despite this, the majority of the scar showed anisotropic structure with FA higher than an isotropic liquid. The analysis revealed that the primary eigenvector orientation at the infarcted wall on average followed the pattern of original fiber orientation (imbrication angle mean: 1.96 ± 11.03° vs. 0.84 ± 1.47°, p = 0.61, and inclination angle range: 111.0 ± 10.7° vs. 112.5 ± 6.8°, p = 0.61, infarcted/control wall), but at a higher transmural gradient of inclination angle that increased with scar transmurality (r = 0.36) and the inverse of wall thickness (r = 0.59). Further, the infarcted wall exhibited a significant increase in both the proportion of left-handed epicardial eigenvectors, and in the angle incoherency. The infarcted human heart demonstrated preservation of primary eigenvector orientation at the thinned region of infarct, consistent with the findings in the porcine hearts.
  
  
  CONCLUSIONS
  The application of high-resolution DTI and LGE-CMR revealed the detailed organization of anisotropic infarct structure at a chronic state. This information enhances our understanding of chronic post-infarction remodeling in large animal and human hearts.
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Farhad
authors.initials: F
authors.lastname: Pashakhanloo
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Herzka
authors.affiliation: Department of Radiology, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Susumu
authors.initials: S
authors.lastname: Mori
authors.affiliation: Department of Medicine, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Muz
authors.initials: M
authors.lastname: Zviman
authors.affiliation: Department of Medicine, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Henry
authors.initials: H
authors.lastname: Halperin
authors.affiliation: Radiology and Imaging Sciences, National Institutes of Health Clinical Center, Bethesda, MD, USA.
authors.forename: Neville
authors.initials: N
authors.lastname: Gai
authors.affiliation: Radiology and Imaging Sciences, National Institutes of Health Clinical Center, Bethesda, MD, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Bluemke
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Natalia A
authors.initials: NA
authors.lastname: Trayanova
authors.affiliation: Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, USA. emcveigh@ucsd.edu.|Department of Medicine, Johns Hopkins University, Baltimore, MD, USA. emcveigh@ucsd.edu.|Departments of Bioengineering, Medicine, Radiology, University of California, 9500 Gilman Drive-MC0412,La Jolla, San Diego, 92093-0412, CA, USA. emcveigh@ucsd.edu.
authors.forename: Elliot R
authors.initials: ER
authors.lastname: McVeigh
mesh_terms: D000369:Aged, 80 and over; D000818:Animals; D016880:Anisotropy; D002908:Chronic Disease; D003287:Contrast Media / Q000008:administration & dosage*; D056324:Diffusion Tensor Imaging; D004195:Disease Models, Animal; D005260:Female; D005355:Fibrosis; D019786:Gadolinium DTPA / Q000008:administration & dosage*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009203:Myocardial Infarction / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D009206:Myocardium / Q000473:pathology; D011237:Predictive Value of Tests; D034421:Sus scrofa; D020257:Ventricular Remodeling
chemical_list: D003287:Contrast Media; D019786:Gadolinium DTPA
keywords: Diffusion tensor imaging; Fiber structure; Late gadolinium enhancement; Microstructural remodeling; Myocardial infarction